FGT - FSW - FAP : Just one vlan blocked

[Bistrol]

Hi,

Infrastructure :

FGT 100F 7.4.7

Core switches : 1024D 7.4.5

Access switches : 148F 7.4.5

AP : 7.4.5

Just one vlan is unavalaible on some switches and some AP after TIER-2.
The root bridge is at TIER-4 on the topology. When i force the root bridge to be at core switch, STP is flapping.

Do you some ideas to resolve this issue ?

Thanks in advance