Hi and welcome to the Chiari forum.
It could mean several things.....one could be that too much bone was removed...and as a result you have cerebral ptosis or brain slump.....it could mean that the patch used sometimes those with Chiari also have Ehlers-Danlos Syndrome which could lead our bodies to reject foreign materials.....if that is the case our bodies can over produce CSF and force the tonsils down and herniate further. AND...your body could just over produce CSF post op for no reason that is obvious.
May I ask why you had two decompressions?