I'm not sure if this is preventable, but all of the placed maps reset in 1.14.3 after using the --forceUpgrade startup flag. Everything seems to be working fine otherwise -- the plugin still loads and images can be placed (or replaced) normally after the fact.

Still the best map plugin out there!

It is most likely that the forceUpgrade removed the map data and thus you need to recreate all maps.

If you have a backup from the pre 1.14.3 map you could try copy the data folder from there to the new map folder. (untested)

I couldn't reproduce the problem on my local CraftBukkit 1.14.3 server, using the --forceUpgrade flag on a 1.13.2 world with maps. Have you tried what Boy132 suggested?

Also try updating your CraftBukkit/Spigot version if you haven't yet. Their 1.14 releases are still flagged as development builds to bugs and breakage is to be expected.

It was a good idea, but unfortunately loading the map data from a backup didn't work either, and I've been keeping up with the Spigot builds. I have a couple dozen worlds between my servers and it happened on all of them rather consistently, but perhaps I was doing something incorrectly. No matter, we're working on replacing them already -- it's not a huge issue. Hopefully I'll be the only one.