Hi axel,
can you share some example code using one of MNE’s example datasets? i.e. if you share some pre-formatted text starting with these lines:
import mne
fpath = mne.datasets.testing.data_path()
fname = fpath / "EGI" / "test_egi.mff"
raw = mne.io.read_raw_egi(fname)
# ...
# the rest of your code that produces the issue
This way anyone here can copy and paste your code into their own python interpretor and help you solve the issue. It will also help us determine if the issue you are describing can be replicated with MNE’s own test files.