I had a same experience but I don’t think its an RX issue. I think its actually the TX of the other side not really transmitting anything.
In my case I have CRS354-48P-4S+2Q+ with QSFP+ breakout cable (FS Q-8LCAO05) on one side and on the other side is CRS328-24P-4S+ with SFP+ module (FS SFP-10GSR-85)
I upgraded the CRS328 from 7.4 to 7.5 and after it booted up, the link was established, CRS328 was reporting RX and TX but CRS354 did not see any RX. Since I did not upgrade/restart CRS354, I am confident the error was on upgraded CRS328 side which was incorrectly reporting TX.
Rest of details I already reported in the 7.5 thread: http://forum.mikrotik.com/t/v7-5-stable-is-released/160518/1