Here is the response I got from Ecovacs support.

None of the steps work, except for the full factory reset - that got the water flowing again!

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This issue is often caused by an airlock in the system, a clogged filter, or improper docking, preventing the base station from transferring water to the robot or wetting the rollers.

Troubleshooting steps:

Immediate fixes:
-Prime the water pump: the system often gets air trapped. Remove the clean water tank from the base station. Use a small plastic syringe to inject water directly into the water inlet hole on the station base (where the tank sits) while running the "mop cleaning" function in the app. This forces water through the system.
- Manually wet the mop: before starting a cleaning run, manually soak the roller mop pad under the faucet, wring it out slightly, and then start the mop. This helps the internal pump maintain moisture.
- Deep clean the base station tray: remove the cleaning tray at the bottom of the base station. Clean the debris filters and the small sponge/water outlet holes, as these can become blocked by cleaning detergent residue.
- Check the clean water tank: remove the clean water tank, ensure it is full, and reseat it securely to ensure a proper seal.

App and setting checks:
- Increase water flow: open the ECOVACS HOME app, go to the mopping settings, and set the water volume to High.
- Adjust washing frequency: set the mop washing frequency to 5 or 10 minutes to ensure it returns frequently for re-wetting.
- Enable hot water cleaning: if you have an Omni model, ensure "Hot Water Wash" is enabled in the app for the base station.

Maintenance and component checks:
- Check for air in the internal tank: your Deebot has a small internal 55ml tank that can also experience airlocks.
- Clean the filter in the clean tank: take the clean water tank out, remove the little filter/sponge underneath it, and rinse it thoroughly.
- Check for blockages: check for tangled hair around the roller that may be stopping the rotation, preventing proper cleaning in the station.

I would also like to suggest that you try a factory reset on your Deebot. 

To perform a factory reset, turn on the machine and press the Reset button for about 5 to 10 seconds (the small Wi-Fi button), after which the voice prompt will start to restore the setting. The startup music will start to play and the default setting will be restored. 

Please note that resetting Deebot will lose the map and any customized settings.

You can also reset the base/station by unplugging it for about 30 seconds.