MikroTik

I had to set up an mAP lite (RBmAPL-2nD) as basic Access Point. In this simple configuration I had to create a bridge and then include in it the two interfaces, but as soon as I inserted the ethernet port I lost connectivity between winbox and the device, in both layer 2 and 3. Just sometime the device was responsive, but for few seconds only. The issue was present only when the device was connected to my MikroTik CSS326-24G switch, in which I manage some different networks using VLANs (but with untagged ports, I use a trunk tagged port also as main line to connect the switch to my MikroTik router that communicate with the VLANs, but this is irrelevant). I don't know if the switch is missconfigured, but every device connected to it works great.
Obiously the PC and the device was connected to the ports of my switch belonging to the same network.
The issue was not present connecting the PC and the device through a simple cheap switch, neither through a professional managed switch without VLANs.
Searching in forums I did not find a solution and finally, after a day of attempts, I solved setting the STP protocol of the bridge to "none" (it was at "RSTP" as default).
I don't know why, but from that moment it works very well.
Can somebody tell me the reason of that? The issue is in the configuration of my switch? is it a bug? Is it normal the need to set the bridge in that way?
Thank you,
Bruno