Ok. Here we go again. NO metal around your APs. Even if you can see the AP. That includes METAL object like LOUDSPEAKERS and CAGES. Also, out a little distance from the brick, concrete, metal wall if you can.
If you tear apart an antenna you’ll find it’s made of metal parts and dielectrics (electrical insulators). So, it should make sense that bringing metal near an antenna can have some adverse affect on how it works.