S+RJ10 won't link up at 10Gb in CCR1072

I have CCR1072-1G-8S+ with 6 x S+RJ10 SFP modules.

CCR1072
Firmware = 6.42.4
RouterOS = 6.42.4

S+RJ10
Firmware = 1.0
Serial = 815D03C31586

I’m connecting these to a Dell N4064 10Gb 48 port switch.

Modules bring link up at 1Gb/s nearly always
Sometimes, the modules link up at 10Gb/s. Once up, they are stable.
I’ve tried 2 metre CAT6A cables. 2 metre CAT6 cables and 2 metre CAT5e cables, no link at 10Gb/s
I’ve tried 3 metre CAT6 cables, link up at 10Gb/s but still sometimes link up at 1Gb/s (1 time out of 4)
I’ve tried 3 and 5 metre CAT6A cables from a different vendor, no link at 10Gb/s
Other devices to Dell switch without any issues at 10Gb/s
Can’t see any errors in log, on either switch or CCR1072.
RouterOS Log says link up (speed 10Gb, full duplex) even when link is up at 1Gb/s - bug?
I’ve also tried several modules. Reseating modules. Fully powering off the router.
I’ve tried turning off auto-negotiation - but this always results in 1Gb/s (and is not the standard anyway).
I’ve sent a supout.rif to support, but no response.

Can you suggest what might be the problem?
My next move is to try another vendor SFP+ module. If they work, the S+RJ10’s are going back :frowning: