No.
The dips in the graph do represent times at which your Pi-hole has received fewer queries, and that Pi-hole did actually process those fewer.
This may just suggest periods of lowered DNS activities, or perhaps that some of your some clients would be by.passing Pi-hole at times.
As with the previous, your most recent debug log does not contain any pointers to Pi-hole crashing.
Quite possibly, your observation does not relate to crashes:
One of your client's has been rate-limited.:
*** [ DIAGNOSING ]: Pi-hole diagnosis messages
count last timestamp type message blob1 blob2
----- ------------------- ----------- ------- ------ ------
1 2023-03-06 18:55:20 RATE_LIMIT 192.168.0.8 1000 60
Pi-hole's web UI would also have alerted you about this.
And if you didn't restart Pi-hole in the meantime, that message should also be still available via Tools | Pi-hole diagnosis.
Rate limiting happens when a client sends excessive amounts of DNS requests.
By chance, your debug log nicely demonstrates this for your 192.168.0.8:
*** [ DIAGNOSING ]: contents of /var/log/pihole
-rw-r--r-- 1 pihole pihole 75K Mar 6 18:58 /var/log/pihole/FTL.log
-----tail of FTL.log------
[2023-03-06 18:55:06.518 983M] Imported 236531 queries from the long-term database
[2023-03-06 18:55:06.523 983M] -> Total DNS queries: 236531
[2023-03-06 18:55:06.523 983M] -> Cached DNS queries: 14405
[2023-03-06 18:55:06.523 983M] -> Forwarded DNS queries: 81680
[2023-03-06 18:55:06.523 983M] -> Blocked DNS queries: 139887
[2023-03-06 18:55:06.523 983M] -> Unknown DNS queries: 0
[2023-03-06 18:55:06.523 983M] -> Unique domains: 2931
[2023-03-06 18:55:06.523 983M] -> Unique clients: 35
[2023-03-06 18:55:06.524 983M] -> Known forward destinations: 2
[2023-03-06 18:56:06.591 983/T1000] Still rate-limiting 192.168.0.8 as it made additional 99363 queries
[2023-03-06 18:57:06.652 983/T1000] Still rate-limiting 192.168.0.8 as it made additional 128788 queries
Note that those would show as spikes in the graph rather than dips.
Commonly., you'd have to investigate your client for reasons why it would send those excessive amounts of DNS requests. In some cases, clients may be desperate for a specific domain that is blocked by Pi-hole, in which case How do I determine what domain an ad is coming from? may help.
Lucky for you, your debug log actually contains a few lines from /var/log/pihole/pihole.log that show one such domain when your client at 192.168.0.8 was being rate limited:
*** [ DIAGNOSING ]: Pi-hole log
-rw-r----- 1 pihole pihole 343M Mar 6 18:58 /var/log/pihole/pihole.log
-----tail of pihole.log------
Mar 6 18:58:53 dnsmasq[983]: config error is REFUSED (EDE: blocked)
Mar 6 18:58:53 dnsmasq[983]: Rate-limiting v7event.stats.avast.com is REFUSED (EDE: blocked)
Mar 6 18:58:53 dnsmasq[983]: query[AAAA] v7event.stats.avast.com from 192.168.0.8
Mar 6 18:58:53 dnsmasq[983]: config error is REFUSED (EDE: blocked)
Mar 6 18:58:53 dnsmasq[983]: Rate-limiting v7event.stats.avast.com is REFUSED (EDE: blocked)
Chances are you should be able to mitigate this. 
In a recent topic, a German user succeeded by configuring a specific reply for those requests, see Probleme mit dem RATE_LIMIT, ein Client sendet zu viele Anfragen - #12 by Keen_Barete.
Let's try to apply their solution to your Pi-hole - please
a) create a custom dnsmasq configuration file, e.g. at /etc/dnsmasq.d/42-block-avast.conf) with the following contents:
# block AVAST telemetry
local=/analytics.ff.avast.com/
local=/v7event.stats.avast.com/
b) exempt above domains (analytics.ff.avast.com, v7event.stats.avast.com) from blocking in Pi-hole via Pi-hole's Domain management
c) restart Pi-hole's DNS resolver via Settings or by running pihole restartdns