After Updating your mod a few chunks get removed and dont get render any more

i found this issue too when updating my mod pack "Friends United" didn't realize it was furnish because I updated a few mods at once. Glad to see you found the problem

Can also confirm this issue

Having the same issue, if you combine any generation mod with furnish it seems to break random chunks?

Hi,
Thanks for reporting.
Really sorry about that! I had made a mistake in some of Furnish rendering code.
The error was fixed in Furnish v21, which is available for download.