It seems problem with power. What switch you have? What is port speed, and what are negotiation settings on port (for speed). What PoE setting is set on port (must be 802.3at, many cheap switches allow (or set by default) limit on port to 802.3af )
R650 has 2.5/1Gbps port, so cabling may be a problem (high resistance diminishes PoE power delivered to AP, or some pair is broken and port does work only on 100 MB/s).
Your other AP probably has less power consumption, different speed negotiation process - so situation you have is completely possible, older AP works Ok, but R650 doesn't.
To be sure, I would try PoE injector (brick), to isolate power issue possibility.
If on same port with power brick R650 will work, than problem is most probably with power settings. If not, power most probably isn't related to issue.
If AP doesn't work with brick, I would check it when connected directly to switch (without cabling). If it will work than, problem is in cabling. If no difference, I wold check with different switch.