This has happened to me a bunch of times over the past month (at least).
Windows 10 server, Firestick 4k client. I finally recorded some evidence.
Logs have been submitted as 44d7db90-08ef-48f6-88a3-3f0582833c94.
I'm playing a recording, go to skip by a commercial and the picture will either freeze of skip back to where I was. Once this has happened, no amount of rebooting or anything will get it working again. The same recording will play fine on my Windows machine. I also just discovered it will play on my non-beta version of the Channels client on my Firestick The old version is 4.6.2.
I hope the logs will tell you something.
I had rebooted both the Firestick and Windows just before my test.
The only strange thing about my system is that the skip ahead button on my remote is set to 1 minute.