Regarding the problems with vsftp, from what I recall OpenWRT folks had some issues when the upgrade was done there too. I actually found these as well:
the bug fix to move from 2.x to 3.0.0:
https://dev.openwrt.org/changeset/31241
later path fixes:
https://github.com/openwrt/packages...8fd5203#diff-9c9c3a2f0d7a62d2e4bba810b6cc3312
I had checked the later patches from Github, but hadn't looked at the older commits from their svn repo. That one doesn't seem related to stability however, but to compile issues, as per this ticket:
https://dev.openwrt.org/ticket/11263