Hello @maykato,
I am unable to replicate the mentioned behavior and also both Jetpack and Speed Optimizer experience no troubles working together.
I would advise you to re-enable the Speed Optimizer and navigate to the Frontend options. There you can try disabling them one by one and testing the page in the meantime. If you notice that deactivating some of the options removed the problem, you can keep that option deactivated or open a Helpdesk request in your SiteGround Client Area so the Technical Support team can investigate further.
Best regards,
Georgi Ganchev
I would advise you to re-enable the Speed Optimizer and navigate to the Frontend options. There you can try disabling them one by one and testing the page in the meantime.
OK, I was able to fix this by disabling all the CSS options under Speed Optimizer > Frontend.
Thank you!