Error: Filename clashes with previously generated name

[Alejandro Bodas (mo-abodas)]

Hi, I'm getting this error in one of my GC5 suites (running on EX):

????????????????????????????????????????????????????????????????????????????????
???!!!???!!!???!!!???!!!???!!!       ERROR        ???!!!???!!!???!!!???!!!???!!!
?  Error code: 1
?  Error message: Filename clashes with previously generated name:
?        /home/users/alejandro.bodas/cylc-run/u-dn073/run1/share/data/History_Data/dn073a.p41988sep
?  Error from processor: 49
?  Error number: 35
????????????????????????????????????????????????????????????????????????????????

?  Error from routine: GET_FILENAME
?  Error message: Filename clashes with previously generated name:
?        /home/users/alejandro.bodas/cylc-run/u-dn073/run1/share/data/History_Data/dn073a.p41988sep
?  Error from processor: 214
?  Error number: 35
????????????????????????????????????????????????????????????????????????????????

I've never encountered this error before. I start from a clean state, so don't understand why it's clashing
with a previously generated name. Does anyone know what could be causing this error? Thanks!