Heya,
first sorry for using such a broad title, I know it's not very helpful...
Anyway here is my issue: After I run the command /wb worldX fill the console does output the process succesfully running, however if i do a /dynmap fullrender, my dynmap is still almost entirely empty.
Here is my output:
`

wb worldX fill
[20:00:06] [Server thread/INFO]: World generation task is ready for world "world X", attempting to process up to 20 chunks per second (default 20). The map will be padded out 208 blocks beyond the border (default 208). Parts of the world whi ch are already fully generated will be skipped.
[20:00:06] [Server thread/INFO]: This process can take a very long time dependin g on the world's border size. Also, depending on the chunk processing rate, play ers will likely experience severe lag for the duration.
[20:00:06] [Server thread/INFO]: You should now use wb fill confirm to start the process.
[20:00:06] [Server thread/INFO]: You can cancel at any time with wb fill cancel, or pause/unpause with wb fill pause.
wb fill confirm
[20:00:13] [Server thread/INFO]: [WorldBorder] world: worldX padding: 208 repe ats: 1 ticks: 1
[20:00:13] [Server thread/INFO]: WorldBorder map generation task for world "worl dX" started.
[20:00:18] [Server thread/INFO]: [WorldBorder] [Fill] 25600 more chunks processe d (25600 total, ~8,8%) (free mem: 4343 MB)
[20:00:23] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processe d (51456 total, ~17,6%) (free mem: 4247 MB)
[20:00:28] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (77312 total, ~26,5%) (free mem: 4618 MB)
[20:00:33] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (103168 total, ~35,3%) (free mem: 4518 MB)
[20:00:38] [Server thread/INFO]: [WorldBorder] [Fill] 25600 more chunks processed (128768 total, ~44,1%) (free mem: 4424 MB)
[20:00:43] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (154624 total, ~52,9%) (free mem: 4265 MB)
[20:00:43] [Server thread/INFO]: [WorldBorder] [Fill] Saving the world to disk, just to be on the safe side. (free mem: 4265 MB)
[20:00:43] [Server thread/WARN]: A manual (plugin-induced) save has been detected while server is configured to auto-save. This may affect performance.
[20:00:48] [Server thread/INFO]: [WorldBorder] [Fill] 25600 more chunks processed (180224 total, ~61,7%) (free mem: 4584 MB)
[20:00:53] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (206080 total, ~70,5%) (free mem: 4477 MB)
[20:00:58] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (231936 total, ~79,4%) (free mem: 4378 MB)
[20:01:04] [Server thread/INFO]: [WorldBorder] [Fill] 25856 more chunks processed (257792 total, ~88,2%) (free mem: 4280 MB)
[20:01:09] [Server thread/INFO]: [WorldBorder] [Fill] 25600 more chunks processed (283392 total, ~97,0%) (free mem: 4187 MB)
[20:01:10] [Server thread/INFO]: [WorldBorder] [Fill] 10915 more chunks processed (294307 total, ~100,0%) (free mem: 4165 MB)
[20:01:10] [Server thread/INFO]: [WorldBorder] [Fill] task successfully completed for world "worldX"! (free mem: 4165 MB)
`

If the WB Fill process completes successfully, the world has definitely been generated out to the specified border. Your problem is therefore presumably with dynmap not having a fully updated map.