WordPress admin intermittently failing – posts not saving

I’m dealing with a really frustrating, recurring issue and I’m hoping someone here has seen this before.

Symptoms (happens multiple times per day):

• wp-admin pages hang or fail to load
• Posts fail to save or publish (Gutenberg spins / “Updating failed”)
• Media uploads fail with: “The server cannot process the image”
• Front-end and admin sometimes return 5xx timeouts
• cPanel / WordPress Manager (Softaculous) throws:
  HTTP 401 – Invalid Security Token (even within minutes of logging in)

What I’ve already checked:

• CloudLinux/LVE usage is well below limits (CPU, memory, I/O, entry processes, no faults)
• Host checked ModSecurity + Immunify360 WAF logs – no blocks
• Disabled All In One WP Security – still happens
• Happens across browsers and devices
• My internet is fine – other sites work normally when this occurs

Hosting environment:

• Shared hosting (hundreds of accounts on the node, per host)
• WordPress site with normal traffic, not a high-traffic spike scenario

What I’m wondering:
Does this pattern usually point to PHP-FPM worker pool saturation, MySQL stalls, disk I/O wait, or noisy-neighbor issues on shared servers?
The cPanel 401 token errors happening at the same time as WordPress failures make me think it’s more than just a WP/plugin problem.

Hosting is with BigScoots on a shared server. I’ve opened multiple support tickets over the past few weeks and so far WAF/ModSecurity checks and plugin-level troubleshooting haven’t identified the cause.

At what point do you stop troubleshooting WordPress and start treating this as a hosting/node stability issue that needs a server move or VPS?

Any insight from people who’ve run into this before would be hugely appreciated.