Typo3 Frontend Performance Issues - Slow Page Loading

For many years, our website, which was built using Typo3, has been experiencing slow performance for the past week.

When we try to visit our site, the loading times are quite slow, sometimes taking 3-4 seconds, while other times it can take up to 1 minute.

There are no performance issues on the backend side; it works properly and quickly as before. No changes have been made to our website in the last 1-2 months. No new posts were added, no plugins were installed, yet suddenly the page loading became very slow, even though nothing was done.

Here are the topics I have researched so far to find a solution:

1. Since we host our website on our own server, there is sufficient disk space, CPU, and RAM available. This has been checked.
2. All log files were checked, and no problems or error reports were found. 3.No new plugins were added, removed, or updated. In other words, no changes were made.
3. Errors and warnings in the php.ini file in the install tools section of the website were corrected. Only the PHP SOAP and ZIP extensions could not be loaded and activated due to our server being old, and we cannot install packages.
4. Using the Typo3 Install Tool interface, everything like Database Analyzer, Clear all cache, Check for broken extensions were checked and run, but we still did not see any errors or improvements.

Our website is hosted on a server running Debian 9.8.0, with 8 vCPUs, 20 GB RAM, and 1 TB disk space. The Typo3 version we are using is Typo3 v6.2.26. So far, we have not been able to find a solution in our research as to why this problem suddenly appeared and how we can fix it. Thank you in advance for your help and suggestions.

Some more Ideas:

• Maybe check https://pagespeed.web.dev/ to get an idea, if the server is the problem or TYPO3
• Check if caching is activated in your TYPO3
• Check browsers console + network analysis for error and problems (very big images, waiting times while loading, blocking / external scripts, blocking css...)
• Check TYPO3 errorlog, maybe it´s very big. If so, delete it
• Check if some tables grown big in your database (logs etc.)
• Check if your website has been hacked
• use the admin panel (not sure if existing in TYPO3 6.2..), to find bottlenecks etc.

And as said before: Update your TYPO3! Beside security issus newer TYPO3 Versions can use newer PHP Version, which could speed up your website too.