The following error was displayed in the data collector job output:
DBG04004I DBP4 16:07:39 REQUEST HTLOCKS FROM *HSTIN*
DBG01014E DBP4 16:07:39 MISSPELLED RESERVED WORD OR LITERAL RLF-LIMIT-TYPE
Release : 20.0
Component : SYSVIEW Performance Management Option for DB2 for z/OS
The problem was caused by the presence of HTLOCK request in the HGHLVL.REQUESTS. Removing it from the .REQUESTS library resolved the problem.