I have an 951G-2HnD operating as the main router in our office connected to a WAP LTE KIT that provides a 4G connection
They are connected by about 30M of good quality cat5E cable. The cable has been tested and restested as good at all speeds and with a range of packet sizes and many millions of packets.. comes up clean every time

However, the two mikrotiks do not seem to be able to negotiate a clean connection.
When I reboot the WAP, I can see it connect on the 951 at 10Mbps and i see lots of errors (in particular FCS)
I have tried setting both ends to not negotiate and to stay at 100mbit full duplex but that has not seemed to work (although I though it had initially as the connection came up raltively clean... once)

if i leave it to auto-negotiate, let it fail, then disable the Ethernet interface at the 951, wait for more than 30 seconds and enable it, it all seems to work ok and can run for days with zero errors (making an obvious hardware failure seem less likely)
software on both is 6.43.4

Anyone else has such problems? How did you troubleshoot/resolve?