I have four totally different TVs (Sony, Samsung, Visio, Visio) with ROKU devices, Express and Ultra. Captions are out of sync on all TVs for some (if not all) episodes of Foyle's War in season 6 and 7.
Unplugging the TV and or ROKU device does NOT repair the problem.
I added the Acorn Channel "via the Roku channel," as opposed to installing the Acorn Channel independently. Closed caption was working great until season 7. Episode 1 was showing wrong words. When I got to season 8, it became apparent that the closed captioning was 1 Season off. Words for S7E1 were from S8E1.
I ended up uninstalling the ROKU Channel, which took Acorn with it. I then searched ACORN and installed that as a new channel (not via Roku Channel) and the closed captioning worked.
I cancelled the "Acorn by Roku" channel subscription without removing the ROKU channel. Then searched for and installed the Acorn channel subscription independently of Roku. CC now works properly for Foyle's War Season 7.
Of course, I probably won't get credit for the remainder of the one month subscription ($5.99) paid on 02/25/21 for the "Acorn by Roku" channel subscription. But then, the remainder of $5.99 is not going to break me AND I was REALLY UNHAPPY watching Foyle's War, one of my favorite shows, without CC. Now that CC is fixed, I consider the unused portion of the $5.99 is worth it.