I have just tested this in 1.19.40 and the issue still remains. It does seem fixed in the current preview version. I have small test and found it deletes any redstone / pistons and glass that is in its way, extended pistons are dropped as items when a fungus is grown near them.
This is now an issue in the live version of the game v1.19.31. it seems to have started after the recent update. The Xbox default keyboard pops up making you have to type in the small window above the keyboard and not directly onto the sign. This also happens with the chat / command window
I can confirm this is an issue playing on realms with Xbox Series S also. Several members of the realm have reported the same issue on other platforms. If it would help I could get more precise data about the platforms players are using. In all cases the text will disappear upon exiting the text editting section before even signing the book. When the book is reopened the pages are blank. I have known in one instance the text reappear in the book sometime later. This is very similar to the sign and anvil renaming bugs and seemed to appear around the same time.
Added photo example, unfortunately screenshots do not show the pop up keyboard.