Tests fail with "XML syntax error on line 7520: invalid UTF-8"

Totals: 1394 passed, 0 failed, 0 skipped, 0 blacklisted, 91ms
********* Finished testing of tst_QStringApiSymmetry *********

agent:2018/02/26 13:17:48 build.go:383: Executing scheduled instruction 1 of 2 - Upload all core dumps if there are some
agent:2018/02/26 13:17:48 build.go:385: 
agent:2018/02/26 13:17:48 build.go:383: Executing scheduled instruction 2 of 2 - Upload test results
agent:2018/02/26 13:17:48 storageclient.go:506: Collecting test results, archiving and uploading them
agent:2018/02/26 13:17:48 result.go:155: Collecting 172 test results ...
agent:2018/02/26 13:17:48 build.go:385: 
agent:2018/02/26 13:17:48 agent.go:181: Test failed
agent:2018/02/26 13:17:48 agent.go:79: ERROR building: error unmarshalling testlib xml output: 'XML syntax error on line 7520: invalid UTF-8'.*no* further _formatting_ is done here

Totals: 112 passed, 0 failed, 11 skipped, 0 blacklisted, 48070ms
********* Finished testing of tst_Bic *********

agent:2018/02/26 17:06:06 build.go:603: 
agent:2018/02/26 17:06:06 build.go:383: Executing scheduled instruction 1 of 2 - Upload all core dumps if there are some
agent:2018/02/26 17:06:06 build.go:385: 
agent:2018/02/26 17:06:06 build.go:383: Executing scheduled instruction 2 of 2 - Upload test results
agent:2018/02/26 17:06:06 storageclient.go:506: Collecting test results, archiving and uploading them
agent:2018/02/26 17:06:06 result.go:155: Collecting 486 test results ...
agent:2018/02/26 17:06:07 build.go:385: 
agent:2018/02/26 17:06:07 agent.go:181: Test failed
agent:2018/02/26 17:06:07 agent.go:79: ERROR building: error unmarshalling testlib xml output: 'XML syntax error on line 7520: invalid UTF-8'.

Totals: 112 passed, 0 failed, 11 skipped, 0 blacklisted, 39338ms
********* Finished testing of tst_Bic *********

agent:2018/02/26 18:11:01 build.go:603: 
agent:2018/02/26 18:11:01 build.go:383: Executing scheduled instruction 1 of 2 - Upload all core dumps if there are some
agent:2018/02/26 18:11:01 build.go:385: 
agent:2018/02/26 18:11:01 build.go:383: Executing scheduled instruction 2 of 2 - Upload test results
agent:2018/02/26 18:11:01 storageclient.go:506: Collecting test results, archiving and uploading them
agent:2018/02/26 18:11:01 result.go:155: Collecting 486 test results ...
agent:2018/02/26 18:11:01 build.go:385: 
agent:2018/02/26 18:11:01 agent.go:181: Test failed
agent:2018/02/26 18:11:01 agent.go:79: ERROR building: error unmarshalling testlib xml output: 'XML syntax error on line 7520: invalid UTF-8'.