U231F access point - aggregated bandwidth of 2 gigabits

I connected a FortiGate 100F to a FortiSwitch 248E-FPOE using four cables to set up a 4-gigabit trunk.

Then, I connected a U231F access point to ports 3 and 4 of this switch, with the network interfaces configured in uplink and LACP enabled to achieve an aggregated bandwidth of 2 gigabits.

I also connected two desktop PCs to ports 29 and 30 on the switch, each with a Gigabit connection. On both PCs, I placed a 3-gigabyte file.

If I start downloading the files simultaneously from two notebooks connected via Wi-Fi to the radio on the 5 GHz band, one of the PCs downloads at 300 Mbps, while the other downloads at nearly zero speed. Once the first download finishes, the second begins. I would expect both notebooks to download the file at the same speed of 300 Mbps.