What is killing my CH341s?

[lekto]

I have a “small” issue, I don’t think it is Gentoo related, but maybe someone here saw something like this.
There are two machines: my main PC and my NAS (repurposed older PC). Both are connected to same wall socket, but NAS is through a UPS. Both are connected to same Ethernet switch. Also, both are connected together with USB capture card (USB to PC, HDMI to NAS), and CH341 (USB to UART, CH341 to PC, serial cable to NAS). Everything was working great, until now.
Recently I bought old Dell D630 to play with, I’m powering it from same UPS, it is connected to same Ethernet switch as PC and NAS, and it was connected it to PC via same CH341 and RS232 cable. Everything is working great.
I wanted to login into NAS using serial console, so I unplugged RS232 from Dell and connected to NAS, but only thing I could see in minicom was trash, that looked like baud rate was off. I restarted NAS, but after that I saw nothing, I reconnected CH341 to USB few times and tried different ports, but minicom started to complain about non existent /dev/ttyUSB0 and IO errors. I thought CH341 is dying - I bought it on Aliexpress in 2017 for ~1$, so it worked longer than I expected. I connected PC to Dell, but that time CH341 worked. Now, I started expecting something wrong with NAS, but when I connected directly (without CH341) Dell to NAS it worked, so looks like something is wrong when connecting PC to NAS. I tried to power NAS without UPS, but same result. I run dmesg -w and at the moment when I plug RS232 cable into CH341 I got errors [1]. After some testing CH341 finally died and it isn’t detected by any of my machines. Luckily I had second exactly same, brand new converter. I swap them, exactly same issue, and now both are dead.
I was thinking maybe both cases had chassis at different voltages, but multimeter showed 0V between them, and since they are connected all time with capture card this can’t be issue.
Any one here saw something like that or have any ideas what is going on?

[1]

[pingtoo]

lekto,

Have you try switch TX and RX?

[lekto]

I use same female-female db9 crossed cable since I bought first CH341, I can't swap RX-TX and I don't think this is issue.