I was having a very similar issue and worked with TAC to isolate and come up with a solution.  Hopefully it helps others. Our environment recently upgraded ASA 5506 to FPR-1010 (running ASA code) and ASA-5515X to FPR-2110 (running ASA code).  The SNM...

Had the exact issue and found our problem - and fixed it! Our neighboring switch to the SG300-28P was a SG500-52P.  We had 2 cat6 copper uplinks going to it.  These ports had PoE enabled.  We discovered by unplugging the power supply on the SG300-28P...