With a VM Hub in modem mode the BQM graph plots the responses from the Netgear Router ( not the VM Hub ).
Wi-Fi is not being provided by the VM Hub, so pay close attention to the functioning of the Tenda Mesh, exactly what happens when the Wi-Fi drops out ? E.g. is that the Mesh is dropping the Wi-Fi signal to change channels ?
Hub Signal Level Checks
Via http://192.168.0.1/ connect to the Hub in Router mode, do not login in, scroll down to "Check router status" Use http://192.168.100.1/ for a Hub in Modem mode
Using the Hub's "Check router status" tabs check the Downstream and Upstream power levels are in spec.
( If already logged in to the Hub menu, the same info is available at : Advanced settings >>> Tools >>> Network status )
Downstream Power Levels of -7 to +7 dBmV are preferred, +10dBmV is the max acceptable, with a SNR of 33dB or higher across all DOCSIS 3.0 channels. Rising error counts across many channels is a current service noise fault.
Upstream Power Levels of 35 to 49 dBmV are preferred, with QAM 64 Modulation mode across all four to six DOCSIS 3.0 channels. Seeing QAM 32/16/QPSK is a current service noise fault. Seeing less than four DOCSIS 3.0 channels is usually a signal level fault.