I recently replaced my Tablo 4th gen and I can’t sign in to it on my IOS app. I reinstalled the app and it won’t let me select “I Have a Tablo Account”.
I should have mentioned that it is on an iPhone SE running version18.5 (22F76)
guess you have not consulted the thread about the outages that have been going on for several days 
While there is a current issue with Guide Data (which we are working hard to resolve), it shouldn’t affect your ablity to sign in.
We recommend reaching out to Support: https://support.tablotv.com/hc/en-us/#contact
FWIW, I have the same issue. iPhone SE, latest Tablo app and I cannot select “I Have a Tablo Account”. I tried the same on my iPad and it works fine and I was able to select it. I did contact Support but there wasn’t really any satisfactory response on the iPhone issue (reboot phone, re-download app, etc). I did attempt those things already without success. Seems like a bug in the app to me. I am going to try on a different iPhone model later on. In any case, the iPad did work for an existing account. Just thought I’d respond on that.