5 Meraki MR24's all running smoothly for two weeks since upgrading to 19.07.7. Many thanks to devs!
Incidentally, to save a bit of time and avoid errors keeping this set of AP's upgraded, since 19.07.4 I've been following the scheme (thanks @cybermaus !) in
which works great to keep dnsmasq, firewall, and odhcpd disabled across upgrades. Looks like this on one of these AP's:
root@ap0:~# ls -l /etc/rc.d | grep disabled
lrwxrwxrwx 1 root root 18 Dec 31 1969 S19dnsmasq -> ../init.d/disabled
lrwxrwxrwx 1 root root 18 Dec 31 1969 S19firewall -> ../init.d/disabled
lrwxrwxrwx 1 root root 18 Dec 31 1969 S35odhcpd -> ../init.d/disabled
root@ap0:~# cat /etc/sysupgrade.conf
## This file contains files and directories that should
## be preserved during an upgrade.
# /etc/example.conf
# /etc/openvpn/
# The following links to a nonexistent file keep these services
# disabled across an upgrade:
/etc/rc.d/S19dnsmasq
/etc/rc.d/S19firewall
/etc/rc.d/S35odhcpd
root@ap0:~#