spigot paper 1.14.4 and PlotSquared-Bukkit-4.303

I have tried to trim and fill plots to the border .

[12:52:00] [Server thread/INFO]: MajorPayne issued server command: /wb TrialWorld trim
[12:52:05] [Server thread/INFO]: MajorPayne issued server command: /wb trim confirm
[12:52:05] [Server thread/INFO]: [WorldBorder] Trimming world beyond border at the command of player "MajorPayne181".
[12:52:09] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.-1.mca
[12:52:09] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.-2.mca
[12:52:09] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.-3.mca
[12:52:09] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.0.mca
[12:52:09] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.1.mca
[12:52:10] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.-3.2.mca
[12:52:10] [Server thread/INFO]: [WorldBorder] [Trim] 6 entire region(s) and 3552 individual chunk(s) trimmed so far (45.6% done)
[12:52:13] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.-1.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.-2.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.-3.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.0.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.1.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] Error! Region file which is outside the border could not be deleted: r.3.2.mca
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] 12 entire region(s) and 7848 individual chunk(s) trimmed so far (100.0% done)
[12:52:14] [Server thread/INFO]: [WorldBorder] [Trim] task successfully completed!

So something else is keeping those regions in memory, preventing them from being deleted. If a server restart and another Trim don't take care of it due to something else still loading those regions, you can always just manually delete the indicated region files for that world while the server is stopped.

So something else is keeping those regions in memory, preventing them from being deleted. If a server restart and another Trim don't take care of it due to something else still loading those regions, you can always just manually delete the indicated region files for that world while the server is stopped.

Dynmap seems to be the plugin keeping worldborder from trimming . I had to disable Dynmap from loading at next reboot , in order for the command /wb trim to not have the error and trim the chunks . Your plugin needs to check and unload the chunks where possible , Dynmap does have customization triggers in the config . Outside of dissabling all of Dynmaps triggers Worldborder is going to conflict from time to time if both plugins are using the same chunk.
Worldborder trim and fill will work on maps that Dynmap has not created a task for and have opened .

I did some more checking , it seems that other things are loading the chunks as well . We have 5 maps and the same thing happened on all maps . For maintenance, I needed to first pause dynmap and purge all maps then disable dynmap , restart server and run the trim command.