You can log in via SSH and check the /etc/config/mwan3 file. The “metric” value determines the priority from 1-WAN (highest), 2-WWAN, 3-tethering, 4-modem (lowest), like this:
config member 'wan_only'
option interface 'wan'
option metric '1'
option weight '3'
config member 'wwan_only'
option interface 'wwan'
option metric '2'
option weight '3'
config member 'tethering_only'
option interface 'tethering'
option metric '3'
option weight '3'
config member 'modem_only'
option interface 'modem'
option metric '4'
option weight '3'
Also, check that the M1 WAN provides a stable Internet connection, so that the router does not switch over to WWAN hotspot.
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