This sounds the same as the issue here Huawei e3372h-325 now working - stuck in CDROM only mode with OpenWrt we have been able to get it working on linux, but not found a reliable solution on openwrt as of yet
Thanks for your follow-up. Unfortunately, I had already come across this thread during my research, much before the one I've opened got merged with it. As you too underline, there aren't resolutive solutions here either (at least for me but it could be due to some kind of mistake on my side, I don't exclude the possibility).
What I was wondering is that usb_modeswitch is installed, invoked etc. still on the extroot setup on that sdcard like everything else so it shouldn't be the culprit because it just doesn't get invoked so no switching happens (at least not by usb_modeswitch): it just seems that the internal card reader doesn't work during boot stage while it works just fine if I leave extroot on the card reader I'm using right now and I put another microsd inside the E3372h (just to mount it and access its contents, that's obvious). Have a nice day! 
Success! it is now working, I connected the dongle to my windows box on a whim and there was an update waiting, following the update it is now successfully picked up as a tethering device on my gl-inet beryl router, connects successfully and passes traffic. The firmware version on the dongle following the update is still showing 3.0.2.61(H057SP7C983) and the WEBUI version is 3.0.2.61(W13SP4C7110) and I can't find any release notes. I have powered off the beryl router several times with and without the dongle attached, the dongle is connecting either way without problem.
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Nice! Congrats!
It was an update provided at gateway web interface?
I've checked it and I don't have any upfrade available 
The upgrade was on the usb dongle, I connected it to my windows box, opened the web interface on 192.168.8.1 then navigated to advanced > updates. It's possible this is a carrier controlled update.
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