When switching back and forth between UMP portlets, the portal will appear to hang indefinitely and stops responding to any input from the user.
The problem seems to manifest most frequently when switching between Unified Dashboard/List View portlets and USM but can happen as a result of switching between any portlets.
During the time the portal is unresponsive, an investigation on the SQL Server will reveal that a query is blocked, and the query will be similar to the following:
select layoutseti0_.layoutSetId as layoutSe1_323_, layoutseti0_.groupId as groupId323_, layoutseti0_.companyId as companyId323_, layoutseti0_.createDate as createDate323_, layoutseti0_.modifiedDate as modified5_323_, layoutseti0_.privateLayout as privateL6_323_, layoutseti0_.logo as logo323_, layoutseti0_.logoId as logoId323_, layoutseti0_.themeId as themeId323_, layoutseti0_.colorSchemeId as colorSc10_323_, layoutseti0_.wapThemeId as wapThemeId323_, layoutseti0_.wapColorSchemeId as wapColo12_323_, layoutseti0_.css as css323_, layoutseti0_.pageCount as pageCount323_, layoutseti0_.settings_ as settings15_323_, layoutseti0_.layoutSetPrototypeUuid as layoutS16_323_, layoutseti0_.layoutSetPrototypeLinkEnabled as layoutS17_323_ from LayoutSet layoutseti0_ where (layoutseti0_.groupId=@P0 )AND(layoutseti0_.privateLayout=@P1 )
Further investigation will reveal that the blocking query is the same or similar query, as if the query is being run multiple times and blocking itself.