Version 1.20.12, same issue. Stops downloading if total download size exceeds 30mb with some random exception.
Version 1.20.11 still not working. Seems to only affect xbox.
Just tried it on 1.20.1, seems to still be an issue.
Update, i found that it works with a limit of around 20mb, but this is very limiting on what you can have. Many texture packs are not this small.
Tried again after the 1.20 update, STILL no fix. I even reduced the download size to ~74mb and people are still freezing. Sometimes they're able to get in with no problem but that seems to be random and rare. Before this problem happened i had worlds with over 330mb download size with little or no impact on loading times or ability to join.
I am having a similar issue. They can only join if the pack is small and doesn't exceed ~90mb, and if I add any add-ons they get stuck near the end. It also loads extremely slow, less than 1mb per second. Most of the people joining are on the Xbox one, and Xbox series S/X. This was not a problem until about a month ago.
I did a bit of experimenting and the limit of download size goes up by a lot if texture packs are not used. So if a resource pack does not replace any minecraft textures (it seems fine if it brings in custom blocks/items) the limit is around 80mb versus the 20-40mb limit when using texture packs. Tested by joining on xbox series x with a PC host.