lucid quartz
Platform and OS version;
Android, and later Windows 10 (to double check)
Running app version;
v4.12.0
Note, the hostage situation did not start until after the update dropped as I was in the midst of doing its prerequisite of comfy clothes, notably there are no hostages to save in recoil ridge, however trotbeck and skarbourg were fine
Steps to recreate the issue
Start making comfy clothes
Wait for servers to go down and game to update
Collect the comfy clothes and start hostage situation
fast pier
I have a similar problem with "Clean Up Your Mess". There were enemies prior to the update, but I wanted to do them after the update. Now they are gone.
lucid quartz
update, i might be going crazy but there are also no *REGULAR silver wolves spawning here in recoil ridge
lucid quartz
update; still no silver wolves 
fallow warren
Same here, no silver wolves respawns or mission silver wolves
spiral coral
same
loud roost
My mission silver wolves for the hostage missions all disappeared too
fallow warren
Update: My mission wolves and other encounters have returned
loud roost
Update: No spawns of either kind have repopulated in recoil ridge. Still bugged. Mission encounter is for “Hostage Situation”
Remains missing as well
lucid quartz
update; I still don't have any silver wolves after the hotfix T_T (i know it wasn't listed, but i had hopes)
hot stratus
I'M FREE
Having the same problem but it sounds like yours is fine? Did you do anything to get them back?
lucid quartz
didn't do anything, though it may have been a fluke as while i managed to complete this mission, the next one requires killing 12 SW groups in "frontier towns" and i could not procc it in recoil ridge (and those SW hasn't returned yet), no SW elsewhere has spawned
just pray yo
loud roost
I had both my mission and encounters return and now they are gone again
