I can’t say for sure, but I’m having this issue too and I’m on siteground. For a while I thought it was WP Rocket causing the issue, but it kept happening even after I disabled it.
Take a look at this
Cant say for sure, but I think I see a trend.
They’re saying it’s Siteground Optimizer, so I guess it’s their cache. Which I guess would explain why it only happens randomly.