Why don't FAPI.UI methods always work out?

Question

Classmates

Good afternoon!
We've been seeing this issue for a few days now.
Sometimes, in different applications, different users experience delays when calling the FAPI.UI.showPayment, FAPI.UI.showInvite, FAPI.UI.showNotification methods, and possibly some other methods, but we can say for sure about these three.
The delay can reach several seconds, and sometimes the request does not work at all (the window with an invitation or with a purchase never appears at all).
This happens from time to time in different games. Because of this, some users cannot pay for some option in the game, send a message to a friend, etc.
Can you please let me know if there is any plan to fix this issue?