diff --git a/meteor/server/api/deviceTriggers/StudioObserver.ts b/meteor/server/api/deviceTriggers/StudioObserver.ts
index ae3b1263c9..5f18675eda 100644
--- a/meteor/server/api/deviceTriggers/StudioObserver.ts
+++ b/meteor/server/api/deviceTriggers/StudioObserver.ts
@@ -212,6 +212,8 @@ export class StudioObserver extends EventEmitter {
 		this.nextProps = undefined
 
 		const { activePlaylistId, activationId } = this.currentProps
+		const rundownContentChanged = this.#rundownContentChanged
+		const pieceInstancesChanged = this.#pieceInstancesChanged
 
 		this.showStyleBaseId = showStyleBaseId
 
@@ -219,7 +221,7 @@ export class StudioObserver extends EventEmitter {
 			logger.silly(`Creating new RundownContentObserver`)
 
 			const obs1 = await RundownContentObserver.create(activePlaylistId, showStyleBaseId, rundownIds, (cache) => {
-				return this.#rundownContentChanged(showStyleBaseId, cache)
+				return rundownContentChanged(showStyleBaseId, cache)
 			})
 
 			return () => {
@@ -228,11 +230,9 @@ export class StudioObserver extends EventEmitter {
 		})
 
 		this.#pieceInstancesLiveQuery = await PieceInstancesObserver.create(activationId, showStyleBaseId, (cache) => {
-			const cleanupChanges = this.#pieceInstancesChanged(showStyleBaseId, cache)
+			const cleanupChanges = pieceInstancesChanged(showStyleBaseId, cache)
 
-			return () => {
-				cleanupChanges?.()
-			}
+			return () => cleanupChanges?.()
 		})
 
 		if (this.#disposed) {
diff --git a/meteor/server/api/deviceTriggers/__tests__/StudioObserver.test.ts b/meteor/server/api/deviceTriggers/__tests__/StudioObserver.test.ts
new file mode 100644
index 0000000000..b2ebaeecc0
--- /dev/null
+++ b/meteor/server/api/deviceTriggers/__tests__/StudioObserver.test.ts
@@ -0,0 +1,156 @@
+import { protectString } from '@sofie-automation/corelib/dist/protectedString'
+import {
+	RundownId,
+	RundownPlaylistActivationId,
+	RundownPlaylistId,
+	ShowStyleBaseId,
+	StudioId,
+} from '@sofie-automation/corelib/dist/dataModel/Ids'
+
+import type { ContentCache as RundownContentCache } from '../reactiveContentCache'
+import type { ContentCache as PieceInstancesContentCache } from '../reactiveContentCacheForPieceInstances'
+import { runAllTimers } from '../../../../__mocks__/helpers/jest'
+
+type OnChangedRundown = (cache: RundownContentCache) => () => void
+type OnChangedPieceInstances = (cache: PieceInstancesContentCache) => () => void
+
+let capturedRundownContentOnChanged: OnChangedRundown | undefined
+let capturedPieceInstancesOnChanged: OnChangedPieceInstances | undefined
+
+jest.mock('../../../publications/lib/observerChain', () => {
+	const fakeHandle = { stop: jest.fn() }
+	const chain: any = {
+		next: jest.fn(() => chain),
+		end: jest.fn(() => fakeHandle),
+	}
+	return {
+		observerChain: jest.fn(() => chain),
+	}
+})
+
+jest.mock('../RundownsObserver', () => {
+	return {
+		RundownsObserver: {
+			create: jest.fn(
+				async (_playlistId: RundownPlaylistId, onChanged: (ids: RundownId[]) => Promise<() => void>) => {
+					// Immediately drive the callback once, to emulate initial observer execution
+					await onChanged([protectString<RundownId>('r0')])
+					return { stop: jest.fn() }
+				}
+			),
+		},
+	}
+})
+
+jest.mock('../RundownContentObserver', () => {
+	return {
+		RundownContentObserver: {
+			create: jest.fn(
+				async (
+					_playlistId: RundownPlaylistId,
+					_showStyleBaseId: ShowStyleBaseId,
+					_rundownIds: RundownId[],
+					onChanged: OnChangedRundown
+				) => {
+					capturedRundownContentOnChanged = onChanged
+					return { stop: jest.fn() }
+				}
+			),
+		},
+	}
+})
+
+jest.mock('../PieceInstancesObserver', () => {
+	return {
+		PieceInstancesObserver: {
+			create: jest.fn(
+				async (
+					_activationId: RundownPlaylistActivationId,
+					_showStyleBaseId: ShowStyleBaseId,
+					onChanged: OnChangedPieceInstances
+				) => {
+					capturedPieceInstancesOnChanged = onChanged
+					return { stop: jest.fn() }
+				}
+			),
+		},
+	}
+})
+
+describe('StudioObserver', () => {
+	beforeEach(() => {
+		jest.useFakeTimers()
+		capturedRundownContentOnChanged = undefined
+		capturedPieceInstancesOnChanged = undefined
+	})
+
+	test('rundown deactivation regression: observer callbacks must not depend on `this` (private fields)', async () => {
+		// Import after mocks are in place
+		const { StudioObserver } = await import('../StudioObserver')
+
+		const studioId = protectString<StudioId>('studio0')
+		const playlistId = protectString<RundownPlaylistId>('playlist0')
+		const activationId = protectString<RundownPlaylistActivationId>('activation0')
+		const rundownId = protectString<RundownId>('rundown0')
+		const showStyleBaseId = protectString<ShowStyleBaseId>('showStyleBase0')
+
+		const rundownCleanup = jest.fn()
+		const pieceCleanup = jest.fn()
+
+		const onRundownContentChanged = jest.fn(
+			(_ssbId: ShowStyleBaseId, _cache: RundownContentCache) => rundownCleanup
+		)
+		const onPieceInstancesChanged = jest.fn(
+			(_ssbId: ShowStyleBaseId, _cache: PieceInstancesContentCache) => pieceCleanup
+		)
+
+		const observer = new StudioObserver(studioId, onRundownContentChanged, onPieceInstancesChanged)
+
+		// Prime state so updateShowStyle goes down the creation path
+		;(observer as any).nextProps = {
+			activePlaylistId: playlistId,
+			activationId,
+			currentRundownId: rundownId,
+		}
+
+		const state = {
+			currentRundown: { _id: rundownId, showStyleBaseId },
+			showStyleBase: { _id: showStyleBaseId },
+		}
+
+		// Trigger the debounced execution
+		const ps: Promise<void> = (observer as any).updateShowStyle.call(state)
+
+		// Flush debounce timers and any queued promises
+		await jest.advanceTimersByTimeAsync(25)
+		await runAllTimers()
+		await ps
+
+		// Ensure we captured callbacks from the two observers
+		expect(capturedRundownContentOnChanged).toBeTruthy()
+		expect(capturedPieceInstancesOnChanged).toBeTruthy()
+
+		const mockRundownCache = {} as any as RundownContentCache
+		const mockPieceInstancesCache = {} as any as PieceInstancesContentCache
+
+		// Regression: invoke callbacks without a bound `this` (simulates lost context)
+		expect(() => capturedRundownContentOnChanged!(mockRundownCache)).not.toThrow()
+		expect(() => capturedPieceInstancesOnChanged!(mockPieceInstancesCache)).not.toThrow()
+
+		// They should return cleanup fns
+		const cleanup1 = capturedRundownContentOnChanged!(mockRundownCache)
+		const cleanup2 = capturedPieceInstancesOnChanged!(mockPieceInstancesCache)
+		expect(typeof cleanup1).toBe('function')
+		expect(typeof cleanup2).toBe('function')
+
+		// Ensure our handlers were called with expected args
+		expect(onRundownContentChanged).toHaveBeenCalledWith(showStyleBaseId, mockRundownCache)
+		expect(onPieceInstancesChanged).toHaveBeenCalledWith(showStyleBaseId, mockPieceInstancesCache)
+
+		// Ensure returned cleanup fns are callable
+		expect(() => cleanup1()).not.toThrow()
+		expect(() => cleanup2()).not.toThrow()
+
+		observer.stop()
+	})
+})