Thank you for your answer. ACC allows to limit the number of days you want the recordings to be kept, what I have done.
In the cams settings, you can also and additionally set the cleaning level for the dedicated partition in the NAS. It is this number that I have set to 98 % I was wondering if the lose of contact for some cams when the partition is full originates from this. In other words, does the Buffalo NAS manages to make sufficient space at time for the new recordings with a cleanup level of 98 % ?
Thanks a lot for your input