Mods:
forge-1.14.4-28.1.70.jar
NaturalProgression-1.14.4-1.0.4.jar

The latest version does not allow to start a server because a client only class is loaded:

https://gist.github.com/Terpo/291a198064363ef20e816cbfba51a8c0

If it helps: In my mod I used an annotation info that prevented loading of an interface on server side:
https://github.com/Terpo/Waterworks/blob/1.14/src/main/java/org/terpo/waterworks/entity/item/EntityFireworkRocketAntiRain.java