Got them all working.
First I tried my RP3 with the latest firmware (
20190103:
https://canaan.io/downloads/software/avalon921/openwrt/20190103/rpi3-modelb/) and this managed to get those 3 miners with newer firmware working, but failed to get other 9 with an older version of firmware to work. So the
statement about Avalon miners and controllers being picky about the firmware version is completely right and it happens both ways.
Then I tried updating the Vidtoo H2 to the latest controller firmware and used the
20190103 ext4 SysUpgrade (
https://canaan.io/downloads/software/avalon921/openwrt/20190103/h3/) file system but this resulted in controller failing to boot up and stuck in an infinite restart. So my Vidtoo controller is dead at this point. Brought it home to see if I can fix it.
Meanwhile, I used my RP3 to update the other 9 miners to the
9211901-faf6d80 (
https://canaan.io/downloads/software/avalon921/mm/2019-01-03/) firmware after disconnecting the 3 miners that are already up to date and each time with 3 of them connected to minimize the risk in case I mess something up. And it went well. RP3 now successfully runs all 12 miners all being on the latest firmware.
One thing to keep in mind is that Vidtoo H2 probably uses SquashFS filesystem so if anyone got a Vidtoo H2 controller you should be extra cautious with upgrading the firmware especially as it seems to have internal memory (along with an SDCard slot) and the default firmware is probably on the internal memory because in my case the SDCard Slot is empty. I need to add that I am not totally sure if it is in fact formatted with SquashFS; what I know is that the 20190103 ext4 SysUpgrade, when applied without removing old settings, will fail. It might be also because I missed something.
... I hadn't heard of anyone using other controllers, where did you order your gear from...
I got my devices from a local distributor; I also failed to find any information about this board. In fact, even Canaan only provides roms for this device in their latest firmware and there is no mention of this device with their older firmwares. My distributor mentioned that these controllers are new so my guess is either Canaan is sending this controller instead of RP with their 2019 batches or that my distributor just jumped on the opportunity to buy a cheaper board as soon as Canaan added support. However, with the controller having a private firmware (a version not available anywhere publicly) there is more chance that this was what Canaan sent to them.
Thank you all guys, specially Steamtyme and NotFuzzyWarm; your suggestions were priceless. Also everyone else for taking the time reading the log file; I know it wasn't easy to follow things and it probably took a lot of time. I am yet to receive a response from Canaan btw.