Had TabloTV gen 2 about a month. Playing recordings generally works, however it seems there is a problem watching a program while it is still recording. Video freezes, “loses its place” and suddenly skips to the end. It does not seem to happen when watching AFTER recording is complete, but I don’t have enough data to know for sure. Happens with Roku TV and AppleTV so I think its specific to playback on TabloTV.
Yes, this is a known shortcoming of the Apple TV app, that from what I’ve read is not likely to be fixed.
It should not be a problem with Roku, however, so you should concentrate on troubleshooting that. Contact @TabloTV for help if necessary.
There is a separate, outstanding problem with Roku that can affect either playback or sound. See here: https://community.tablotv.com/t/update-on-4th-generation-tablo-compatibility-with-roku-os-14
Had TabloTV gen 2 about a month.
To avoid confusion here, be aware it’s called “4th gen” 
FYI…we watched a show last night on our Gen4 device via Roku while it was recording. We had to go to the Library and select All Shows, then click on the show we wanted to watch. It wouldn’t let us from the list of Latest recordings. I may have some of my tab names wrong because I’m not in front of the device at the moment.
I had this issue with FireStick. My Gen 2 died (I think–perhaps just the HD) and now I have a Gen 4. Haven’t really seen this issue yet.