Hi David life was a little busy lately. Forums are a great place for problems like this.
Me too only purchasing a DAC in last couple of years, then Roon. Still some vinyl sounds better 
It sounds like you are clicking “Add To Library” to download but it’s failing. At one point I had to log out of Tidal in Roon under settings, services then reboot my Roon Core. Then log back into Tidal before it would let me play/ show local files. If that doesn’t work. You could try rebooting your internet modem and or router but if only Tidal gives trouble that might not be effective. If you are connected wirelessly that could cause problems like you describe, if your device is too far away from base or there are brick or concrete walls involved. 300 feet in a big empty gymnasium LOL
Roon Community has a support section that will ask some questions about your setup and they will help out. I have gigabit internet for work and have never had trouble other then as described above.