Admin console/ssh stops working shortly after boot, only if it is acting DNS server

Expected Behaviour:

[Pi-hole should be accessible]

Actual Behaviour:

_[I have a Pi 3 B running Raspian Buster, in which I installed Pi-hole. It keeps locking up after a few hours to a day and becomes unresponsive, no display or ssh access. The only way to remedy is to power cycle the unit. This is happening on 2 separate Pi 3 B's. Any help would be appreciated.

Here are the details:

OS: Buster - Full
SD Card: 16GB Micro SD HC
It is connected via Ethernet

I have connected a keyboard/mouse/monitor and the Pi does not respond or display anything. This is the case for both of my Pi 3's. This only occurs when I have my router using them as the DNS server. If they are not providing any DNS filtering then they run forever without issue. The only way to get them working again when they lock up is to powercycle them. They still work, per say, when it locks up, but no gui is accessible to try and remedy the situation.]_

Debug Token:

_[I took a log using journalctl -f to see what happens when the gui becomes unresponsive and have included it, or at least a section, as it generated a 2.5gb log over 2 days.

piologs -]_

Please send us the token generated by

pihole -d

or do it through the Web interface:

Here is the token:

Taking a look at your appended journalctl excerpts, it seems you are experiencing difficulties with your SD card:

Feb 08 22:30:07 raspberrypi dnsmasq[906]: reply is
Feb 08 22:30:08 raspberrypi kernel: [0;1;31m[0;1;39m[0;1;31mmmc0: card never left busy state
Feb 08 22:30:08 raspberrypi kernel: [0;1;31m[0;1;39m[0;1;31mmmc0: error -110 whilst initialising SD card

A quick research for the error brings up two scenarios:

  1. an incompatibilty between your SD card, the SD card controller and the driver for that controller
    This could possibly be fixed by an update of the driver, normally provided through your OS (a number of Ubuntu releases seem to have suffered from this in the past)
  2. your SD card is corrupted
    This could comprise of only a few blocks not written correctly (e.g. in a low power situation) or a substantial amount of blocks through wear-out by heavy workloads or just time of duty.
In either case, I'd recommend switching to another SD card (click for details).

ref. 1. :
If it is an incompatibilty issue, you'd have to look and wait for an update through Raspbian.
I don't consider this likely, as you would not be the only one with this problem, but you may start with upgrading your installation to the most current level:

sudo apt-get update
sudo apt-get upgrade

ref. 2.:
As your SD card does not fail completely (RPi works after reboot), I'd say that only a few blocks of your SD card are affected.

You may get lucky by just reformatting your SD card.

I would nevertheless strongly suggest using that card only for storing songs or pictures on a smartphone (where you could take the risk of losing a song).

You should also check your RPi's log for under-voltage warnings:

grep -i "voltage" /var/log/syslog

If this returns such warnings, you need a better power supply.

I have replaced the Micro SD card the Pi/Pi-hole has been running smoothly for 5 days now. It appears that the SD card was the issue, and that is very weird that I had 2 Pi's with the same issue

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