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...