My two cents.
It’s hard coming home to a situation where you’re under the “watch” of “mom and dad” after you have moved out, moved to another state and a situation where you are now living with a GF and living daily your own life. Unless you can come home and be fully treated as that adult you are living every other day of the week, it’s awkward.
It could be that something is less than perfect in his live. But if he wants to share he’s going to have to be comfortable to share - not judged. Cause whatever is wrong? Largely - as an adult - it’s his thing to handle. That doesn’t mean he doesn’t need the support of mom and dad but he doesn’t need one/two more people to have to please in the situation.
What you describe sounds like a household this week that has been tight and terse. Relax! Do what you would normally do! Try and spoil him a bit - not with $ and big gifts but offer to make some hot chocolate when you’re watching a movie, make his favorite breakfast.
Thank him for helping you this morning with the UPS drop off. Offer a coffee shop stop for a 20 minute reprieve. I think it’s ok to say “I sense that something is up” BUT not in a judging “spill the beans” way. Be like a friend not a mom. Let him know you miss him - him as a human being - and let him know while it’s a transition for you too, you can be a good listener (IF you can be - you are going to have to also work to change your role/relationship from parent to “a caring family member who loves and enjoys you”.
If he wants to come home for Christmas, help him make it happen. Maybe he can split costs. Don’t be keeping a $$$ tab. Keep a love and support tab - and don’t let that pot ever run out.