What really complicates your issues is that this bug doesn't affect all Roku devices as I'm able to rewind just fine with Paramount Plus on my Roku Ultra, my Roku Express (older version than yours), and my Roku 3. And unfortunately, issues that don't affect all Rokus take longer to resolve.
What I think has happened is that for some reason the newer Roku Express models with Paramount Plus have some type of memory issue that causes your Rokus to crash when you press the rewind button. The reason I'm speculating on this is because my Express had memory issues which prevented me from loading the YouTube channel until that was finally resolved with an update.
Since this appears to affect your specific Roku models, you should contact Paramount Plus and let them know your specific Roku devices are having this crashing issue and see if they can provide an update that fixes this. Since this issue appears with the Paramount Plus standalone channel app, unless you have to use that because you're linking this with your provider, you could instead cancel Paramount Plus through their website and sign up through another service such as Paramount Plus with Showtime through the Roku channel. I've listed others that carry Paramount Plus in one of my posts above. The only other option is to either use a Roku device that's not affected (meaning not using your Express -- unless this bug affects all Roku devices if you're unlucky to have gotten it with an update) or using a non-Roku device.
You could try this, but it probably won't solve anything: go to Settings/System/Advance system settings/Advance display settings and turn off Auto-adjust display refresh rate. My old Express model doesn't have this setting, but perhaps your newer Express models have this, and it could be causing the crash to occur. If you don't see this setting, then your Roku model doesn't have this. You could also try to adjust the Settings/Display type, so for instance, if you're using 4K, try 1080p instead or 720p to see if that stops the issue.
There may be workarounds such as pressing the fast-forward button and then quickly pressing the rewind button, pressing pause before pressing rewind, or pressing the up and/or down key before pressing rewind, but I don't know if these would work since I'm not experiencing this issue. Until this is resolved, you may have to restart the show by pressing the up key twice while watching the show and pressing OK and then fast forward to the part you want to rewatch to avoid a crash.
Sorry I couldn't be more helpful. I tried to change settings on my Rokus in an attempt at replicating this issue, but I couldn't figure out a way to get my Rokus to crash when pressing the rewind button on Paramount Plus.
