RADIUS doesn't work with management vlan for first switch only

I have a RADIUS server which works for 3 of my 4 switches and I don't understand why.

192.168.18.1

192.168.18.2

192.168.18.3

192.168.18.4

18.2, 18.3, 18.4, works fine, the radius sees they and the AUTH is ok, but for 18.1 it doesn't work. The error message on ther RADIUS server is coming from the ip 192.168.15.3 which is the managment ip for the MPSL of the main switch there. I don't understand why can't the RADIUS pick up the ips of the management of the first switch.