ESI include injects entire page HTML instead of ESI block code


New Member
Hello! I'm waiting to hear back from LitesSpeed support about this, but I thought I would post in here too in case it's something others have experienced.
In short, I'm working on a WordPress site that's running on lightspeed server through Hostinger.

I've included an ESI block in a page template following this documentation to the letter:

It generally works as intended for a few minutes - in this case, showing "Hello World" and then a random number with a ttl of 300ms (I've also tested nocache). After a few minutes, if I go to the page in a fresh browser, it'll load slower than usual and dump the entire homepage of the site in where the ESI block is supposed to be.

Things I've tried so far:
Purging the cache (ESI block works again for a few minutes and then breaks)
Disabling cloudflare entirely (no effect)
Trying to turn ESI on in .htaccess (I'm not sure this is even a thing but it didn't do anything)
Changing the location/name of the ESI block (result is always the same)

My only guess is there's something conflicting with the caching or server config, or a stray wordpress plugin that I'll have to track down, but let me know if you've seen this before! Thanks in advance.