In the starting area, on the deity selector, Tyche is not listed. Tymora is, however.
I chose Tymora since it was on the living deity list on the chooser, but it wouldn't allow me to cast spells then. A DM set me to Beshaba, same issue. Once set to Waukeen it works fine now, however...
Seems to me that the issue is that Tymora and Beshaba are tagged as dead gods, as should be the case, but Tyche was never added to the list of viable deities, so you can't make the proper choice.
I just remembered Acacia Vigne (Tychaen cleric played by Thomas) who didn't have any issues with casting divine spells.
I thought of Acacia, but I'm not so sure how thomas was able to select Tyche as I looked on the list and didn't see it. Perhaps I missed it, but it gets confusing that both Tymora and Beshaba are still there, when they probably shouldn't be.
Usually Priests have to put their deity in the box during character creation. I am guessing that is how Thomas did it, you don't need to use the selector if you have it already set.
I put Tyche in on creation, then tried to set using the chooser in the start area because it instructs you to do so. Though when I logged in I got a message that Tyche is not a valid deity. Just trying to keep everything I did clear so in case this is a problem that needs fixing it's all fully understood.
If you select the deity at creation using your deity field there should be no problem even if you don't use the placeable. It should tell you that - even if unlisted - Tyche is a suitable FR deity etc etc.