@julian is that one of the changes?
the 2 lines I ran was literally this (as root):
systemctl stop nodebb; git fetch; git checkout v1.5.x; git merge origin/v1.5.x; ./nodebb upgrade; systemctl start nodebb
wait a minute and the forum works, without an issue (upgrading from v1.4.6 to v1.5.3)
next (as root):
systemctl stop nodebb; git fetch; git checkout v1.6.x; git merge origin/v1.6.x; ./nodebb upgrade; systemctl start nodebb
File ownership is not correct (might be due to extra files not being there, due to older release) and once ownership is corrected, pages get stuck until it is refreshed.
Should I try a different branch, maybe?