Oneplus 6 (8gb/128gb) SIM & Wifi disappears & phone reboots randomly frequently. What to do?

Oneplus 6 (8gb/128gb) worked perfectly fine from July 2018 to Nov 2022. Now, problems start appearing. There are 2 separate problems - SIM & Wifi disappear & Phone reboot at random frequency. I am not sure whether the problems are linked or not. Important point - + Using original DASH charger since day 1, running original Battery (battery health also OK). + As the problem worsens, time between restarts reduces from 30-40 minutes to 2-3 minutes & sometimes few seconds (sometimes it restarts at Oneplus logo loading screen). + Phone feels slighlty heated up to the left of Fingerprint sensor ---------- Kindly note - ## *I have tried all the troubleshooting steps-network reset, factory reset, OS downgrade etc* *Nearby repair shop (DOUBTFUL) - Network IC reset, Motherboard repair etc.* ---------- **DETAILED SCENARIO** --------------------- In Nov 2022, Phone started randomly losing network - SIMs as well as WiFi - I changed SIM cards it started working correctly. Now after few days, the problem reappeared & frequency increased. In Dec 2022, Phone started restarting abruptly during normal usage. It is generally coupled with NETWORK LOSS as well. Now, I performed regular troubleshooting steps as mentioned above to no avail. Then gave phone to a trusted nearby repair shop to only temporary relief. Total 3 visits to repair shop - 1st Visit - He told that Network IC issue was there. New NW IC ₹ 2000/- *Result*-Worked absolutely correctly for few hours. HAPPY!!! Then same cycle of Network Loss & Random restart & then working fine randomly & then problem again. 2nd Visit - Told that seems like 'Motherboard' problem. Repair/Refurbished MB ₹ 2500/- more *Result*-Worked absolutely correctly for 48-72 hours. Elated & HAPPY!!! Flashed Lineage OS & thought everything is normal now. And demon came back again - the same cycle of Network Loss & Random restart & then working fine randomly & then problem again. 3rd Visit (April 2023)- Told that there might be some pending issue, I will check thoroughly again for 3 days & use. NO CHARGES. *Result*-Got phone back after 15 days, worked fine on WiFi till it got discharged to 8-9% & I put it on charge using DASH Charger. The same cycle has again started. **I am clueless** When the phone works, it works like a charm - but suddenly, network loss & phone restart keeps happening. Please help Stackexchange community.