I very rarely get XP from reading material in the game with the latest patch. I am using the GoG version, through GoG Galaxy with auto updating on. Here is what I found through investigation

I started a new game after the latest patch came out. I very rarely see XP from reading material, as far as I can tell I am only getting XP from reading material that is quest related.

When I put back in my old saves before the new patch was released and I read all the written material I had in my inventory and I get XP for every single one of them. I went a picked up some new written material and I got XP for them.

So it looks like your fix for the XP for written material was only a fix for games started before the patch, but it has not been fixed for games that started after the patch came out.

I have noticed that a) The xp gain message only appears after the book/note is closed, and b) that it does not seem to appear if I spend more than a few seconds reading. I suspect it is only a display issue (the message expires after the standard time, but is only set to display after the book is closed, hence no message if the book is closed after expiry), but it is hard to check since your total xp are not listed as a numerical value anywhere. Try closing the book quickly and see if you get the xp message then - you can always reopen it immediately afterwards.

I think you're correct. Most likely the xp gained notification actually pops up in the background, but it's not visible while the book is open- therefore if you spend too long before closing it you never see the xp gain.

Also, images don't give xp.