/ip firewall mangle add action=change-mss chain=forward new-mss=clamp-to-pmtu passthrough=yes protocol=tcp tcp-flags=syn
Same trouble here accessing websites. Adding that chain to mangle made our nightmare go away.
Same here... We noticed issues when temps dropped below -30 F. We are operating hundreds of nodes in East Central Minnesota USA. Boards come preset w/ cpu-setting on power save. We changed our settings to regular and have not seen a cold weather drop out since.