The bug
In the 1.19.50 update, the changelog mentioned that the Witch Hut is set as 'Surface spawner'. While not written down, this change also affected the Pillager Outpost.

This change fixed MCPE-154877, but introduced this new issue.

Since the pillagers from an outpost spawn as 'Surface' mobs, they will share the mob cap with (regular) pillagers that spawn inside a raid and patrol. So, when you start a raid, no new captain will be able to spawn in the outpost, if there are regular pillagers in the area.

This issue does not occur with pillagers riding a ravagers don't (as they take up the 'cave' cap, and thus not share the same cap)

Steps to reproduce
1. Open Pillagers Testing 1.20.10.24.mcworld(Only works in 1.20.10.24+)
2. Press the structure block that spawns a regular pillager
3. Watch through the glass how captains are not able to spawn
4. Kill the pillager riding the ravager and see how captains are able to spawn again
5. Repeat step 2 till 5 with the structure block of the patrol pillager
Note: You can use the command blocks to kill the pillagers

Extra steps
You can also use the first structure block to summon the pillager riding a ravager that spawned inside a raid. You can watch how captains are able to spawn while the pillager + ravager is alive.

Expected Result
Here is a table of what is expected (whether they are surface/cave means they share the same cap)

Or

If either these ways were implemented, the game would keep on spawning captains (as the different types of pillagers don't share a mobcap with the ones from the outpost)

Observed Result

This information is based on the idea that the Outpost, Patrol and Raid pillagers share the same cap (no captain spawns), because the only change that happened was for the outpost pillagers since 1.19.50

Media
Video about the steps to reproduce: https://youtu.be/b2nV4eVVk7E

Possible fixes
There are a couple of fixes possible:

1. Change the pillagers from the raid and patrols to 'Cave'
2. Revert the change of the Outpost (Make it a 'Cave' spawner again (if this is the only change, then the older issue (https://bugs.mojang.com/browse/MCPE-154877) will be introduced again)
   Change the pillagers on the ravager to 'Surface' spawns