Thanks again @meaton for all the helpful replies!As I said I would do, I tried to reproduce it a lot of times, including uploading big files (3GB, 5GB) and it didn't reproduce on my Mac.However, at the customer, it reproduced easily, even with small files - she tries to upload 3 files of ~10mb each, and it happens.I checked again her Console logs, and no sign for utun_output or ctl_enqueuembuf, but those line seems related:default 17:27:22.110479 -0400 symptomsd NWPath: kNetworkPrimary NWPathStatusSatisfied interface en1 index 6 default 17:27:22.110535 -0400 symptomsd primary interface change to en1, type 1 default 17:27:22.110692 -0400 symptomsd Primary change default 17:27:22.110754 -0400 symptomsd noi: NOI: v:0 type:Wifi, isAny:yes, isBuiltin:no, loi:-1, flags:0, event: kNotificationNewPrimaryInterface, oldLoadedLqm: 100, rawLoadedLqm: 100, newLoadedLqm: 100, not posting default 17:27:22.118243 -0400 apsd Looking up connection on peer: d573aec0 found default 17:27:22.118320 -0400 apsd Looking up connection