I'd put a cable tester on the cable, you could have one pin shorted to another or oxidation on one of the pins, either way different devices will react differently. The MR could have dropped down to 100Mb/s (dark green on core switch port in dashboard), but the MS might not be set to allow negotiation down below 1Gb/s. I recently had an issue with some cabling I did where I had a short between pin 3 (B, so the positive data signal for one direction) and the shield that allowed an IP phone or AP to work, but only at 100Mb/s...
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