To reproduce this issue go to Preferences=>Folder Tabs=>Tab Groups, select a group and click Edit. Now select one of the tabs, click Edit Format=>Labels=>Create a new label filter and create a label filter like Date=>Match=>modified=>within 1 day. Click OK=>OK. Going back to the Labels site of the selected tab you'll see that the label filter is gone.
I didn't test if the other options of this folder format dialog are working.
Confirmed, the same here. The new labels won´t stick.
Many thanks for fixing this in v11.8.4 (beta).