Adding Tidal tracks to your library does not copy the audio to your computer (we don't have license to do that), so they're always streaming in real-time from Tidal.
It's likely that either Tidal is delivering content too slowly (this happens from time to time--they are scaling out aggressively right now, and don't always keep pace with their quickly growing user-base), or that your network connection to them isn't sufficient to keep up with the stream.
Roon aggressively preloads tidal streams to the greatest extent that we are permitted to. This smooths out a lot of issues when compared to, say, the Tidal web player running in FLAC mode, but until their servers are rock solid, we're a little bit at their mercy here.
Just in case something else is going on, @kevin can you please help @Evo1668 grab some logs? Just want to make sure that my guess matches the reality.