issue with managed fortiswitches

hello all, i have 6 floors in a company , each floor has 2 or 3 edge switches and each office in the floor has a small tp-link switch (5port) that compine the PCs, and this small switch connected to the edge and all floors connected to two core switches working as MCLAG and all the switches are managed by fortigate.

i have 3 connection connected direct to the fortigate (ADSL , MPLS , Leased Line).

on the fortigate i have configured a vlan for each floor , when i enable these vlans and assign them to each floor i found a big packet loss in the network but when i work with one vlan for all floors all thing work fine with no isuue.

can anyone help with this issue?