Switch disconnecting frequently

facing an issue with one of the access switch is going offline again and again. 

Fortigate as a controller running a on 6.4.9

Core Switch 1048E running v 6.4.11

Access Switch 124F running v6.4.11

Ntp is synced. only on switch 124F is having an issue.

core switch connected as MCLAG Peers other access swi has below configuration

config switch trunk
edit "E48T0000000213-0"   ----->>>>> to another Core SW 1048E
set mode lacp-active
set auto-isl 1
set mclag-icl enable
set members "port45"
next
edit "G6H00000000"  ------->>>  TO Fortigate
set auto-isl 1
set fortilink 1
set mclag enable
set members "port48"
next
edit "4FF00000009417-0"  -------------->>>> Access Sw 124F connected
set mode lacp-active
set auto-isl 1
set mclag enable
set members "port2"
next

 **************************************

************* Troubled switch logs 

connectivity