Could be a bug or corrupt save file:

After the crown is lost on Island 5 and on returning to the island, the Population has doubled or trippled... some knights and archers just stood around in groups and did nothing the entite time at the castle the boat building area, this may have something to do with the boat being loaded when the crown was lost?.......

continued anyway....

and....

On attacking the cave portal no troops joined in the bomb attack effectively making it impossible to do so, as a result unable to complete the Deadlands campaign....

Windows 10 latest version.

So I reloaded the game today after several days of not playing it as I considered it impossible to complete now...
and low a behold the last knights I created on the cave side turned up to escort the bomb (I know this as they were the ones who were wiped out in the explosion), there were no night attacks maybe because the cave portal was already destroyed and 3 nights may not have yet past?

On entering the cave having paid the 5 coins it was an easy task to overcome the defenders, destroy the nests and arm the bomb at the hive, however for a quick escape the bat skill wouldnt work and the mount was rather slow, never the less having stopped several times to attempt a bat change the Gamigin still managed to get to the exist in time, maybe this is an island 5 thing? as i got blown up last time i tried to escape on this beast on island 3...

Note: these problems have been resolved.