I am having the same isue as well w/ the $4.99 essential package. I called Roku tech support and the steps they had me go through are worthless. I suspect that Roku may have some kind of an add blocker that causes this error to occur.
I absolutely know the issue is w/ the advertisments b/c if I view movie or series clips or extra's the issue does not occur b/c in this content is no advertisments.
I also tried logging in to my Paramount+ account from my desktop computer. I then stream to my Chromecast to my TV and have no issues.
Also my daughter has Apple TV and the same $4.99 package and has no issues.
I however try the Paramount+ app on my iphone and I get,"Fatal Error" , due to licensing restrictions this video isn't available in your location (5408). So this issue appears to be on more than one platform.