Replacement hub 3 issue

At the beginning of January my connection speed dropped off a cliff from the normal 400Gbps to less than 0.5Gbs.  Around half the downstream channels were showing error counts in the millions.  After a conversation with customer service a new hub3 was dispatched and when installed fixed the speed issues.

Unfortunately the new Hub about once a day stops communicating then reboots itself knocking me offline for around 10 minutes. Sometimes this happens at night when there is little consequence but I often work from home and need a stable connection.  There is nothing in the network log to indicate the reboot or a reason for it and all channels are connecting with near 0 errors and 32dB SNR or greater.

And after the third time this happened while on an important work Teams call I phoned customer service again.  After going through a factory reset and asking me if I still have the issue (how can I tell right after A reboot if the once a day random reboot was fixed???) and me telling them no they have arranged an engineer visit for Tuesday but I am now concerned that the engineer will not be able to do anything as it is likely just the hub that is fault and being a very intermittent issue will not be able to find an issue with with it.  I'm worried that if the engineer decides there is nothing wrong I will be charged for it.  

Should I phone customer service again and insist they just try sending me another replacement hub rather than the engineer visit?  When I called them I got the distinct impression they didn't actually listen to what I was telling them as none of it followed their script which they were determined to follow.