We do not provide support for "hybrid" servers that hack Forge together with Bukkit or it's derivatives.
If you can reproduce the issue using a stock Forge server please provide a debug.log from it.
This is possible but requires the usage of the "workDir" command line argument every time you run the Minecraft Launcher in order to be effective.
More Info: https://minecraft.fandom.com/wiki/Minecraft_Launcher#Command_line_usage