Try using smartpack kernel manager (root required) and set the CPU frequency on the big cores to 1.8ghz and 1.5ghz on the little cores. The H990DS variant in particular tends to have higher peak power draw than other variants in situations where cell reception is poor. Which can cause instability. Underclocking the CPU seems to help.Since I don't play any games anymore on my phone since Clash Royale many, many years ago, the most intensive thing that I do it's occasionally video-calling via Telegram FOSS. But let me tell about my history with this V20 H990DS
I bought this device used, and the seller said that the battery needed to be replaced, and randomly it gave me green-screen reboot messages when below 30% and the thermals wasn't great because it was the end of summer here in Brazil. Since everywhere that I searched about buying new LG batteries anyone tells that it's hard to find a real original and reliable I decided to try this one from Aliexpress, and also ordered some copper shims (0.5mm and 0.6mm) to put thermal paste and improve things. And a 128GB SDcard since it was cheap now (compared to years ago... I tested with H2testw and it works perfectly)
So the battery arrived first, and even before it arrived I installed the Lineage 19 and with the new 4.X Kernel it almost never gave me more green-screen reboots, but few random reboots when below 35%.
With Lineage 18 + SwanKernel Extreme gave the most stable scenario but only one time I did try to video-call with Telegram and it went stable, but slow (probably due underclock, maybe?)
But last Friday using the new battery I tried to video-call through Telegram some relatives that live abroad, and with only 5 minutes of calling it rebooted and was warm-ish? So the copper shims arrived early that week and I decided to do the thermal mod this week.
With the 0.6mm it pressed the LCD giving a darker spot, so I decided to replace with the 0.5mm, put new thermal paste and try again... So no dark spot on the screen.
I installed Telegram on other computer and tried to call and test the V20, but it still reboots after some time, but the strange thing it never reaches 62 or higher.
I tried the CPU Throttling Test to test the thermals and it barely reaches 60 with the Extreme+Gaming or with only Extreme as well.
So after all of this, I remember that H990DS have the reputation for drawing a lot of power:
1) Even a "compatible non OEM" battery can't provide what this device demands in terms of power consumption?
2) Having a dual-sim gives me freedom in terms of separate personal-work calls etc and not having to carry 2 phones. Could a dual sim card adapter could be a better approach?
3) There's a chance that this H990DS motherboard it's problematic/defective somehow and replacing with another H990DS would fix things (or even a H990 non-DS with that dual-sim adapter)?
4) The random reboots could give some useful information somehow for you devs? And how the best way to collect it?
5) Are video-calling that demanding, even if it don't reach the same temperatures that the pure CPU stress?
6) Any tips, suggestions?
PS: @xxseva44 sorry I couldn't give you the logs, but the instability/problems here are taking much more time that I initially planned.