The port does not come up when assembling LACP between FortiSwitch 1024E and 148F.

[Vivus]

Hello everyone.
I have five Fortinet devices:
1 x FortiGate 120G
2 x FortiSwitch 1024E (SW01-C and SW02-C)
2 x FortiSwitch 148F (SW03-A and SW04-A)

FortiLink is configured to manage switches on ports X1–X4, which are connected to ports 19 and 23 on the FortiSwitch 1024E.
I've also created an MCLAG between the two 1024Es on ports 25 and 26.
I'm currently trying to create an LACP connection between the core and access ports. The connections are as follows:
SW01-C port2 → SW03-A port49
SW01-C port17 → SW04-A port50
SW02-C port2 → SW04-A port49
SW02-C port17 → SW03-A port50
After connecting the patch cords, everything worked automatically, but port 49 on SW03-A doesn't work at all.
I've tried changing cables, ports, and settings—to no avail.
I'd appreciate any ideas or tips on where to look.
I'm attaching a screenshot of the diagram below.

 

[Vivus]

For clarity, I will add the configuration outputs:

SW01-C (trunk) # show
config switch trunk
edit "E24TF25003255-0"
set description "MCLAG-TO-SW02"
set mode lacp-active
set auto-isl 1
set mclag-icl enable
set members "port25" "port26"
next
edit "G120GTK25019861"
set description "Fortilink-TO-FG"
set auto-isl 1
set fortilink 1
set mclag enable
set members "port19" "port23"
next
edit "8FNTF25003610-0"
set mode lacp-active
set auto-isl 1
set mclag enable
set members "port17"
next
edit "8FNTF25002242-0"
set mode lacp-active
set auto-isl 1
set mclag enable
set members "port2"
next
end

SW02-C # show switch trunk
config switch trunk
edit "E24TF25003235-0"
set description "MCLAG-TO-SW01"
set mode lacp-active
set auto-isl 1
set mclag-icl enable
set members "port25" "port26"
next
edit "G120GTK25019861"
set description "Fortilink-TO-FG"
set auto-isl 1
set fortilink 1
set mclag enable
set members "port19" "port23"
next
edit "8FNTF25003610-0"
set mode lacp-active
set auto-isl 1
set mclag enable
set members "port2"
next
edit "8FNTF25002242-0"
set mode lacp-active
set auto-isl 1
set mclag enable
set members "port17"
next
end

SW03-A (trunk) # show
config switch trunk
edit "_FlInK1_MLAG0_"
set mode lacp-active
set auto-isl 1
set members "port49" "port50"
next
end

SW04-A # show switch trunk
config switch trunk
edit "_FlInK1_MLAG0_"
set mode lacp-active
set auto-isl 1
set members "port49" "port50"
next
end