convert_efield2voltage.py Error in <TTreeCache::FillBuffer>

[lwpiotr]

Sometimes, when analysing a lot of files/events, we get:

Error in <TTreeCache::FillBuffer>: Inconsistency: fCurrentClusterStart=0 fEntryCurrent=176 fNextClusterStart=178 but fEntryCurrent should not be in between the two

Analysing the files on which it happens separately does not seem to cause the error.

According to this old ROOT thread:
https://root-forum.cern.ch/t/inconsistency-error-message-in-ttreecache-fillbuffer-when-using-clonetree-and-ttreereader/35152/2
This indicates only reduced performance. But it would be nice to figure out what is the problem at some point.