Help interpreting measurements Duntech Pcl 500, null in the 7k range

Hello,

i'm asking help to intrepet the measurements i took yesterday in my room with a calibrated UMIK 1 mic.
It's a well treated room, measuring 3.9m width, 5m lenght e 2,2m height. The Ceiling is made of a light layer of wood (so i guess very bass frequencies travel above that) and the room is at the first floor of an old house.
My listening area sits at 38% circa of the lenght of the room, speakers are placed in equilateral triangle near the front wall, just after the acoustic panels

I'm getting cancelations at 122Hz 480Hz 1000Hz 1900Hz which i think could be caused by a room mode, but not shure.
What i'm not understanding is the massive null that occurs in the 7,6 / 8 kHz range, which doesn't show in the single speakers measurements.
I add screenshots of SPL and expecially Phase measurements wich I can't interpret practically.
I add a measurement of the LR after the correction with Ik Multimedia Arc Usb, tuned to my preferred listening target curve.
I last add a photo of the studio. In the measurements the bass traps are right behind the speakers, and there was absorbent material (Isolmix) in the reflections points of the desk and under the desk

Thank You Really much

Ludovico

Thank you all for the kind responses. I'm pretty sure the speakers are equidistant but maybe microphone placement wasn't. I'll check again and let you know.