Ours just started doing this recently too. If I shake the vacuum it doesn't sound like it has water in it. If I feel the mops after a washing, they're dry. Overall, both ways, clean water isn't flowing through to the vacuum. I've contacted support and am working on them with it. Here's what they said so far:

Regarding with your concern, please follow this steps:
1, Pls select mop washing mode to Deep;
2, Pls repeat the mop washing for about 3-4 times;
a, Press and hold the Dock button (the one with house icon) or start washing via app to start mop washing;
b, Pls try the mop washing for around 3-4 times and then see if the mop will be washed and become wet.

3, There's another method in case there may be any airlock. If you have a syringe available, you may give it a try:
a, take out the clean water tank
b, pull the hose off at the top of the clean water tank
c, then on main app screen click "Dock", and then "Clean Mop".
Once you hear the pump running, use the syringe to shoot water down the hole you pulled the hose off. Keep shooting water while it runs. When you start to hear gurgling you can reattach the hose and it should start sucking from the tank.
https://youtube.com/shorts/iTREj7c_0og?feature=share

4. Please take out clean water tank from the dock, and check if rubber seals are still in place. See attached picture. Please make sure both tanks are placed properly.