This article describes about the reason SRX380 is disconnected after upgrade. 

On SRX380 fxp0 was reusing first data port (most likely ge-0/0/0) MAC address and therefore causes an overlap. This was fixed in platform PR1770775
 
Once after the bug was fixed, this caused issue in mist side where the logic of getting mac was not working as expected ( Oc-term subtracts 1 from first MAC and calls it Identity MAC. )  
 
Issue affects when device is upgraded to any version above the below mentioned.
20.2R3-S9, 20.4R3-S10, 21.2R3-S8, 21.4R3-S6, 22.1R3-S5, 22.2R3-S3, 22.3R3-S2, 22.4R3-S2, 23.2R2, 23.2R2-S1, 23.4R1, 23.4R2, 24.1R1
 
On kafka logs we can see oc-reject reason being mac-address changed.

This is now being fixed in mist backend.