MR2100 internet connection always dropped while falling back to 3G network due to poor 4G signal

Hi,

I'm a frequent travller between LA, TX, Japan and Taiwan. I bought the M2 device at Hong Kong around four months ago, and I have MR1100 at the same time.

The issue here is my MR2100 router is unhappy now after its f/w update to NTGX24_10.16.03.00, before that the device work perfect with original factory f/w but I forgot to note which version.

Now the unhappy device will drop internet connection intermittently even I turned off all power saving/sleep related function, the only way to get it back is to do reboot.

This is not the only problem, my on-going session might bump into problem easily somehow, the most siginificant observation is voice call delay or frozn several seconds and reconnected back. Even in a fair/good connection quality like RSPP -88dBm/RSRQ -11dBm/RS-SINR 10 dBm. and the RS-SINR will be weird sometimes like 0 or -2 in a short time.

The most critical problem is the internet connection will be dropped easily while driving through a poor signal area, with the same ISP vendor my MR1100 will keep connection on 3G network but MR2100 will drop connection and lost network a while and then back to 3G network, it will stay at 3G network even good 4G signal is available. The only way to get it back to 4G is to reboot.

Is there any way to roll back to previous factory firmware (I knew there are several issues on eariler version)? I'm not sure if above observations are HW problems or fw problems, the connection performace/reliability is my iphone Xs Max > my Android phone > HP DragonFly notebook with Intel XMM7560 LTE-A Pro >= MR1100 > MR2100.

Please help to save my unhappy MR2100~