Apple IPhone 6 - Loses range - full-> one dot-> no network-> full

Hello, I have an IPhone 6 which is losing range cyclically, it looks like that when the phone is turned on the maximum range (5 dots) after about a minute falls to one dot, then "no network" and again the maximum (5 dots).

I was doing:
restore in DFU - no changes
I moved the board to another body with tapes, antennas, etc. - no change
I warmed up with hot air around the baseband - no change. Imei is always available, not lost.

I did not just change the antenna cable that is on the other side of the board - I checked its continuity with the meter and it's OK. Unfortunately, I do not have a replacement at the moment.

I tested on the card with Orange and play because I currently have one.

Did anyone have such a case?

Turn off the 4G mode and see if something changes?

There are many possibilities because the whole GSM / LTE track is very extensive.

If there is a change after switching off 4G and the range stabilizes, I would look for U_WTR_RF LTE modem and its U_QPOET power supply.

If nothing changes, start from the end, i.e. hybrids U_ASM_RF

Also verify the Baseband chip itself, especially the RFEE1_DATA signal

Strange things are happening, I have tilted up a few contacts in the sim slot and on Orange it easily switches between 2g, 3G, 4g. It has improved significantly, sometimes it will lose the range, but my 6Plus also happens to lose the network for a moment (Play) so it considers it normal.

Does such a lack of a sim contact can cause such circuses with range? It seemed to me that if the card did not touch, I would receive the message "no sim"

Short-term failure to contact any of the contacts in the slot of the sim card may cause problems with coverage and not give a message about the lack of a sim card.