We have since discovered the error that you are seeing in the forum admin profile form is the same as the one you fixed but needs a separate fix of it’s own. You can find explicit details and explanation in this post https://simple-press.com/support-forum/sp5-general-topics/new-user-problems-performance-options-bug/page-3/#p156955
We are still a bit mystified about this as it only seems to effect a very small number of users bit this will fix it and this fix is in the next SP update.
Now question regarding the numerics on the end of the display names. I see you have the display name set to the WP login name (your first attached image). If you look at the users in the WP Users (all Users) admin screen do the names have numerics on them there? And when these people post to your forums do the display names have numerics showing up?
I am not sure what else to ask to be honest. SP is not adding those numbers on the end buit it would be really nice to try and find out where and what is doing it,