I replaced RB4011 with RB5009 and I get rapid flapping with 1G Mikrotik BiDi modules. Only if I set them to 1G - when set to auto negotiate, they do not connect at all. I have a new 70m cable there (old one got damaged) and in the meantime upgraded the router. Signals are fine, from -4,7 to -6 dBm, ...