I checked the log on one of the master AP's, seems the CAPWAP tunnel gets restarted for some reason or another.
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.4366] UBIFS: reserved for root: 3682397 bytes (3596 KiB)
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.4366] UBIFS: media format: w4/r0 (latest is w4/r0), UUID D36509B8-8343-4919-8651-B8C56A82B3A6, small LPT model
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.4931] UBIFS: un-mount UBI device 0, volume 0
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.4931] UBIFS: background thread "ubifs_bgt0_0" stops
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.5006] Image Data Request sent to 10.x.x.x
Mar 6 12:17:18 kernel: [*03/06/2020 12:17:18.5588] CAPWAP HW tunnel params changed, DELETING the existing
Mar 6 12:17:19 kernel: [*03/06/2020 12:17:19.6149] HW CAPWAP tunnel is ADDED
Mar 6 12:17:58 kernel: [*03/06/2020 12:17:22.2454] ........
Mar 6 12:18:15 kernel: [*03/06/2020 12:18:03.8860] ...Re-Tx Count=1, Max Re-Tx Value=5, SendSeqNum=100, NumofPendingMsgs=3
Mar 6 12:18:15 kernel: [*03/06/2020 12:18:15.5474]
Mar 6 12:18:18 kernel: [*03/06/2020 12:18:18.3983] Re-Tx Count=2, Max Re-Tx Value=5, SendSeqNum=100, NumofPendingMsgs=3
Mar 6 12:18:18 kernel: [*03/06/2020 12:18:18.3983]
Mar 6 12:18:21 kernel: [*03/06/2020 12:18:19.4311] .Re-Tx Count=3, Max Re-Tx Value=5, SendSeqNum=100, NumofPendingMsgs=3
Mar 6 12:18:21 kernel: [*03/06/2020 12:18:21.2492]
Mar 6 12:18:24 kernel: [*03/06/2020 12:18:24.1000] Re-Tx Count=4, Max Re-Tx Value=5, SendSeqNum=100, NumofPendingMsgs=3
Mar 6 12:18:24 kernel: [*03/06/2020 12:18:24.1000]
Mar 6 12:18:26 kernel: [*03/06/2020 12:18:24.8193] .Re-Tx Count=5, Max Re-Tx Value=5, SendSeqNum=104, NumofPendingMsgs=7
Mar 6 12:18:26 kernel: [*03/06/2020 12:18:26.9510]
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.8018] Re-Tx Count=6, Max Re-Tx Value=5, SendSeqNum=104, NumofPendingMsgs=7
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.8018]
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.8018] Max retransmission count exceeded, going back to DISCOVER mode.
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.8025]
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.8025] CAPWAP State: DTLS Teardown
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9155] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9156] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9157] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9158] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9164] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:29 kernel: [*03/06/2020 12:18:29.9165] DOT11_DRV[0]: vendor_send_mgmt_frame VAP 2 is not up as expected
Mar 6 12:18:30 NCI: CLEANAIR: Slot 0 CAPWAP down
Mar 6 12:18:30 NCI: I0: shutdownNci
Mar 6 12:18:30 NCI: CLEANAIR: Slot 1 CAPWAP down
Mar 6 12:18:30 NCI: I1: shutdownNci
Mar 6 12:18:30 kernel: [*03/06/2020 12:18:30.9242] Dropping dtls packet since session is not established. Peer 10.x.x.x-5246, Local 10.x.x.x-5256, conn (nil)
Mar 6 12:18:30 kernel: [*03/06/2020 12:18:30.9243] Dropping dtls packet since session is not established. Peer 10.x.x.x-5246, Local 10.x.x.x-5256, conn (nil)