I've noticed this happen sometimes but not other times. When it happens and you don't see the spells to cast, there is a work-around. Instead of hitting "Resolve", click on each of the exile zones (the swirl next to your library and your opponent's library) and you'll be able to select the spell to cast from there.

Coming back to follow up. It happened to me in main phase 2 as well, but I clicked on the Exile Piles when resolving the trigger (before hitting the orange button) and it let me click the spell that was just exiled to cast it

I've experienced this as well, but notably I think I was unable to cast spells main phase 1, but in main phase 2 I was able to? In a game against Heliod I cast Etali and exiled spells Main 1, an Ajani and Azusa were exiled and I was unable to cast them. I was confused and clicked through to Main 2 before copying Etali, and I could cast the spells I exiled with the second Etali. Then in a separate game against Magda, I specifically cast and copied Etali both Main 1, and was unable to cast either set of spells I exiled.

Same for me

Experiencing the same

Experiencing the same