Hi Anton,
I’ve checked your website and here you are my recommendations:
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Update all installed plugins and of course the WordPress itself to the latest stable version.
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If you’re using a CDN, please clear the CDN’s cache and disable optimization services.
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Reset your htaccess file by renaming it to .htaccess-bak
. Then in WP Admin Menu, go to Settings > Permalinks and just click the Save Changes button.
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Increase the PHP Memory Limit of your server. Click here for more detailed information and how to increase the PHP memory limit.
If none of these helped, then please provide us with FTP login details in a Secure Note so we can investigate this issue in details.
Thanks.