This has been seen happening ever since we have upgraded to 4.9.345.0 version.
The issue is happening when there are large number of columns (probably > 10) masked by a same masking functions and if the user makes any changes to that function and tries to save it, it keeps on spinning. The only way the user gets out of the situation is by refreshing the page. The function is 'not masked', by the way.
The issue is tried after reboots too. Once or twice for a tag that was applied to very few tables, the system returns back.
Release : 4.9
Component : TDM Web Portal
This is resolved in TDMWeb-4.9.356.0 or greater.