Did you try MR tech support? I know their technical expertise level has gone down ever since they got bought by SH but would be still be good to highlight to them the issues so that they can improve the service. I'll be doing that tomorrow as the quality of my VOIP calls is still laggy despite the improved ethernet speed test results.
Its weekend, I don't think they are working. The connection at last came back on this afternoon, more than 12 hours after last night. Right before I was going to change back to AXE300. All connectios were the same as last night, just restart the ONT. It used to went down for some tens of minutes, only came back up after numerous restart of the ONT, but that didn't work last night.
Its obviously MR side that causing these disconnections, sometime it shown connected but no internet access--router shown "Cold Standby", as oppose to "Hot standby"--ready to take over when the other WAN is down. I had used MR 1Gbps back in early and mid 2010s, never had such issue.
My take is do not use MR hyperspeed as your only internet connection, use a backup. I will call MR to see if I can cancel the service since it can't even maintain stable connection, a shame in 2020's.
Edited: 2320hrs, it went down again, can't even maintain connection for 10Hours, what more can I say?