One thing I've learned in this game. If people want to take out something for points or other motivations they will and it doesn't matter how much you pile in it. Sometimes the more you load in the more they want to hit it. It be my Presidio atm. We aren't the biggest group in the tides but we do have our fun both in peace and war time.
We have held it for some months so I can rule out the captured and retaken scenario.
I also looked through the individual garrisons each member has at the P. I do not see those numbers on anyone's garrisons.
lastly I checked the troop movements section back until 22-01-2019 where it cuts off. I don't see those numbers sent in any of them. What day did you send them? Did you send them all at once? Did they just disappear overnight and you had them piled in over time?
Are you sure you didn't recall them to your haven? As ElDevilDog stated they auto-harbor when returning.
Did you also look under the "My Garrison's" tab in your stronghold? There should be a Presidio reinforcement under there and you can send/recall from there if you find them showing up.