WIFI broken, MM 6.0.1 DBT version SM-N915FY

my wifi is broken after 5-10 seconds and comes back, than again brocken. tested with stock rom and custom. bootloader is MM.
thats correctly firmware " N915FYXXU1DPE1_N915FYDBT1DPE1_N915FYXXU1DPC3 " now...
can any help please?

ps: mobile phone is very clean and without scratches or breaks. never dropped !!!

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