tempdb: filegroup is full while space is available both in filegroup & transaction log

SqlServer 2014 sp2cu2: having troubles with tempdb (350Gb full size: 8x25Gb primary group + 150 Gb log).
Error is Msg 1105, Level 17, State 2 Could not allocate space for object 'dbo.SORT temporary run storage: ..422202655866..' in database 'tempdb' b