WP login HTTP ERROR 500

Hi! I had the same problem with two sites hosted by Strato on the current WordPress version (5.1) – suddenly and without having updated WP or one of the plugins:

500
Internal server error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at service@webmailer.de to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.

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The solution is, PHP Boost turn off. This can be found at Strato under Databases and Webspace / Set PHP version. The (then working) PHP version is currently 7.2 for me.

Regards
People