Asuswrt-Merlin 380.65 is now available for all supported models.
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One potential new issue seem to be specific to MIPS models (RT-N66U/RT-AC66U) and their older kernel.
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This is another sign that it might be time to retire these older models...
I have RT-N66R, and it failed to update from 380.64_2. (I don't expect it to be related to the issue mentioned.)
I tried twice. Both times it was upgrading, not giving any errors or messages, but when it booted up, I could see the old version remaining (as seen everywhere, including the system log).
Any suggestions?
PS.
Please, do not stop your efforts for the *66*. It would be a waste to throw away this still capable router.