Issues after migration

Hello everyone.
I’m having a wee-bit of an issue trying to diagnose my very random intermittent issue of losing site connectivity.
It’s a client website that was developed on my own hosting and is actually still live without any glitches, it was successfully migrated and had run normally for the first few days. Then client contacts me to let me know the site is unreachable.
An error message sometimes appears
“The page you are looking for is temporarily unavailable.
Please try again later.
5d59414802b3ed9239b91082789fc0b6 6ab0777de7b0b7723c9466893ffdf3b6 e5414a60aaaacb0f081d5685ea9c74d6”
Considering the site is a migration and the “original” are supposed to be carbon copies, nothing aside from hosting (server configs) makes sense, or am I mistaken?

Here are some details on what I’ve tested and what’s been done
– pinging server – success
– loading other website located on server – success
– website speed test – intermittent results from 2 sec load time all the way to “site down”
– online status checks – online or down with, no pattern discernible.
– bumping wordpress memory to a whopping 1024MB – didn’t need it on development environment and also is overkill as the backend usage didn’t seem to go over 20%
– reaching out to Ionos (client’s host) to try to understand what’s going on, their support ran me a list of generic issues that I’ve pretty much looked over, so no real help, aside from saying server resources could be limited for the type of website (hmmm).
– site health check points to SQL server being outdated 5.5.x instead 5.6.x (not sure if that would cause service intermittence or slowdowns) and the imagick module (not installed or not enabled)
– php running latest 7.4.x
– wordpress at latest version so are the plugins

List of plugins used:
– elemetor/pro, theplus addon
– wordfence – scan frequency is default
– updraftbackup (schedule is once biweekly)

What I’ve not done yet is disable plugins and enable them individually that would prove a plugin is the issue though it wouldn’t explain why I still have no glitches on my development env.
I also thought I could start by keeping the strict essential for site functionality, turning off firewall/backup plugins – that’s about the only extra I’m using.
Also, not certain if flipping debug to enabled will point to much as WP hasn’t complained about anything…
Ionos have a the crappiest interface/user panel for managing one’s site, access to logs is extremely limited to just site visitors and support didn’t want to send me them (what?). Despite fully understanding that hosts are in no obligation to help with WP but c’mon, logs to the server, that’s a bare minimum.

Everything is pointing to server issues but I’m not sure what else I can do. The worst of it all is the client is absolutely illiterate in these matters and thinks I “broke” it.

Thanks for reading this guys, I really appreciate it and I apologize in advance for the length. I’m at a total loss at possible solutions and now, money..

The page I need help with: [log in to see the link]