Memtest86+ 5.01 is crashing with any of 2 RAM modules

I've been using a

  • ASUS H110M-R BIOS Ver. 1802
  • Intel Core i5-6400 CPU @ 2.70GHz
  • RAM Kingston 8192MB 2133 MHz

for around 3 years without issues. First Ubuntu 18.04, then 20.04 Updated Around a year ago I added another RAM module Kingston 16384MB 2133MHz.
No issues too until a couple of weeks ago I started having problems: after a day or two system slows down until freezes, sometimes with error notices about javascript ( Chrome or Thunderbird ) I guess they are only the last visible part of the problem.
Today I ran memorytest86+. It freezed at 23% of the first test.
Next I removed the 16GB RAM module and it froze at 34%.

Next I replaced the 16GNB module by the 8GB one. It froze at 61%.

UEFI X.M.P is disabled.

Here's what I wrote in a note some days ago:

An hour ago I got another freeze. Clock freezes at 15:33 and I rebooted at 15:44.
Here are the events I see in syslog during that time.
Oct 18 15:31:52 Ubuntu_20_04 thunderbird.desktop[4293]: JavaScript error: resource:///modules/AddrBookCard.jsm, line 197: NS_ERROR_NOT_AVAILABLE: PreferDisplayName: undefined - not a boolean.
Oct 18 15:33:23 Ubuntu_20_04 systemd1: Started Run anacron jobs.
Oct 18 15:33:23 Ubuntu_20_04 anacron[50624]: Anacron 2.3 started on 2021-10-18.
Oct 18 15:33:23 Ubuntu_20_04 anacron[50624]: Normal exit (0 jobs run).
Oct 18 15:33:23 Ubuntu_20_04 systemd1: anacron.service: Succeeded.
Oct 18 15:33:39 Ubuntu_20_04 thunderbird.desktop[4293]: [2021-10-18T18:33:39Z ERROR style::stylesheets::rule_parser] Saw @import rule, but no way to trigger the load.
Oct 18 15:36:06 Ubuntu_20_04 /usr/lib/gdm3/gdm-x-session[1352]: (II) event4 - KYE Wireless Mouse: SYN_DROPPED event - some input events have been lost.
Oct 18 15:44:01 Ubuntu_20_04 kernel: [ 0.000000] microcode: microcode updated early to revision 0xea, date = 2021-01-25

What else to check? What could be bad?

Update 1:
Main UEFI BIOS.
uefi main
Advanced tab.
adv

A couple of times after changing hardware config I got this screen. I just pressed F1 to enter main UEFI menu, then ESC and sys load was okay. I haven't set anything about overlocking, I don't need this.
dps changes


Remove all hardware except RAM. Then test the RAM modules one at a time (only have 1 in the system at once) and then run Memtest.

If all of them pass, it could be a bad RAM slot other than the first one, but you know it's not the RAM. Test the rest of the slots. If all of them pass no matter what the slot, it's some other hardware causing the problem, such as your graphics card.

If none of them pass, either your first RAM slot is bad or it's a power issue. Try replacing or temporarily using a different power supply.

If at this point, problems exist even with a different power supply, replace the motherboard.