flarumacc I found the pages extension on the list with not compatible extensions for release 16. [...]
Just tried it yesterday and [...]
You install an extension that is known to not be compatible with beta 16 on a Flarum beta 16 installation. So, what do you expect except some errors?
Yes, despite not having tried myself that has to be expected.
Have a look here: https://extiverse.com/ to find out which extensions are compatible with beta 16 and install only one of these on a Flarum beta 16 installation.