Here also no issues on setting curtains on a certain percentage via GUI and/or the Flow card.
How to fix for your case has also been mentioned in the posts you mention (you probably read the ones in the app store) on that it doesn’t work for them, contact forest support (iot@forestgroup.com)
Revert isn’t possible.
This indicates that earlier paired devices are not 100% compatible. In that case, deleting the device and fresh pairing should do the trick. BTW, the message that you used deprecated features should have been a clue, so be sure to mention that next time.