Entering caves on a friend's world causes character to rollback.

Mods I was using were Status Announcements, Combined Status, Geometric Placement, Abigail Keybinds, SmartCrockPot, Dusk and Night Music, Gesture Wheel, and my friend was running no mods.
For reproducing, I'm just going to list the events that happened leading up to the rollback since I have no idea how easily it can be replicated.

1. We load into the world, in the previous session we had killed Queen Bee, Moose Goose, Eye of Terror, and Spider Queen.

2. As we're back at base, frog rain happens, and we easily take care of it with Abigail.

3. We finally decide to go boating, so we set up the boat and sail around until we run into the lunar islands.

4. Hang around the lunar islands for a bit until we've gotten enough glass swords, stone fruit bushes, and bull kelp.

5. Friend wants to change character as summer is beginning to approach. I go into the caves and get lightbulbs when it happens for the first time.

6. All my gear and items were reset back to the previous session which was in the middle of winter. I had a thermal stone and all my rain gear was 100% durability, and my character was also in the winter set of clothing since I change my cosmetics a lot.

7. I leave the caves and my items didn't reset back, they remained the same as the caves.

8. Mildly frustrated I get more resources to prepare for Summer, and my friend finally changes off of wortox to wx-78

9. We get the resources, I precraft Alc Engine, Crock pot, Ice box, and a chest, and also grab all of our food, and head down into the caves.

10. Same thing as step 6 happens, except this time I also lose all of my pre crafts as well. At this point I logged off frustrated.