WP Website is shown in HTML

I‘ve been experiencing quite a strange issue with my WP website since I’ve upgraded my WP to the version 5.4.2.

From time to time (it can occur to 2-3 times / week) my Website is displayed as html Code on all the devices / in all the browsers (pls take a look at the Screenshot). The problem disappears as soon as I log in into the WP dashboard – no further actions are required.

I‘ve checked the plug-ins – they are all compatible. There are also no errors detected in the WP Website Status.

Has anyone any hint for me what could cause such a problem?

Thanks in advance.

Kind regards,
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