i had the same thing happen to me try this
sudo apt-mark unhold hostapd ......not needed if you didn't put in on hold
sudo systemctl enable hostapd.service
sudo nano /home/pi/.openplotter/openplotter.conf
change version = 1.2.0 to 1.0.0, mine was blank after update fail.
ctrl x y enter
reboot
try update again
sudo apt-mark unhold hostapd ......not needed if you didn't put in on hold
sudo systemctl enable hostapd.service
sudo nano /home/pi/.openplotter/openplotter.conf
change version = 1.2.0 to 1.0.0, mine was blank after update fail.
ctrl x y enter
reboot
try update again