Ran into this issue as well. Looks like your on Nexcess (I am too). I found this fix: https://www.commercegurus.com/docs/cart-checkout/nexcess-empty-mini-cart/
In WordPress, go to Nexcess > Dashboard > Settings
For me, I turned ON “Enable WooCommerce cart Fragments”
When I first built my site, I had to turn this setting OFF like it says in the link above, which fixed it at the time, but I just had the issue again and so now I turned it ON and it fixed it.
Funnily enough the setting used to be “Disable WooCommerce Cart Fragments” and now it says “Enable WooCommerce Cart Fragments”
So maybe they changed the “direction” of the setting and now it needs to be on, not off.
Anyhow, see if that fixes it for you.
