EPA 524.2 Dibromochloromethane and Bromoform failing high for PT only

I run EPA 524.2 using 7890B/5977B GCMS with a 4760 OI Eclipse purge and trap. The column is an Agilent 121-1324 DB-624. Recently I have failed two PTs for dibromochloromethane and bromoform. Both failed slightly high out of range (less than 0.5ppb). However, all LFB checks pass and are not biased high. I have seen these analytes fail low and know the appropriate troubleshooting. Has anyone encountered this issue? Thank you in advance for any advice.

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