Confirmed on Realms for 1.21.0
Confirmed on Realms for 1.20.80
Still Occurs in Realms 1.20.60, It seems that It will go a long while without occurring then once it starts (I often am editing many signs in a batch for storage chests or markets) it continues to do it.
I really cant see any pattern as one sign will be okay but another sign with the same text or same text with one word added will cause the #### to appear
Confirmed for Realms 1.20.12
Slavic names written in Cyrillic almost 100% cause this issue. After writing in sign, if sign does not glitch out immediately, I have not seen any glitch at a later time so issue seems to occur during the moment that the sign loads after editing.
Just want to add that I am having this same issue.
A way to sometimes fix the issue is to download the world, change the resolution settings there, replace the world then set the resolution again. then restart game then join. but only sometimes, then after a few days the issue reappears.
Edit: If you check "Require players to accept resource packs to join", it also does not stay checked. so maybe the issue is with realms not saving settings?
Confirmed for 19w07a
Confirmed in 1.21.50 via duplication of @ShadeTC's method (Just trying for consistency in reported occurrences)
Don't know why this was marked as resolved, unless it has to do with the transfer to the new bug reporting site