Help needed with some Wordpress-related issues

Tarjouspyynnön kuvaus

Hello,

I've been keeping this Wordpress website up for some years. I'm stuck now with some issues, of which three more urgent ones. I'll describe them first in one line, then more extensively. If you feel comfortable fixing only some of the issues, that's fine, but even better if you can fix all at once.

1. mySql database has been exploding recently, probably because of some unnecessary log saving.
2. WP keeps telling me I need to use a persistent object cache. My website provider is ovh.com.
3. A scan on semrush apparently indicates issues with 'mixed content', which could be bad for my seo/sem.
*Then a few less urgent things, but would be nice to have them solved*
4. "Page cash is detected but server response time is still slow"
5. "A scheduled event is late. The scheduled event, action_scheduler_run_queue, is late to run. Your site still works, but this may indicate that scheduling posts or automated updates may not work as intended."
6. I would like to have reCAPTCHA set up for my contact forms, but don't succeed.

Below I describe those issues more extensively. Here first some extra info:
- A few months ago I wanted to clean up my website to make it faster. I de-activated almost all plugins, only activated those I really need and got rid of the others. The website was then superfast (confirmed also by to Gtmetrix). But not for long, so some things are not like they should.
- The website has a simple webshop, which is directly connected to my POS/BMS software

1. mySql database is exploding. This happened almost two years ago as well. The database has been keeping a stable size of less than 100Mb, but suddenly with every backup it significantly increases in size, to soon get over its maximum limit of 400Mb. The problem returned apparently after 'cleaning up' my website as described above. Probably I overwrote the fix that one guy had made then. The issue was just a few lines of the database exploding in size. This is what he wrote back then:
"So as I suspected there are issues of LOG files being saved into the database. This is caused by different plugins including woocommerce itself and WPFORM lite. So this means that there are many scheduled actions running on the background. I can check to reduce the retention period of every running hooks to 1 day or 1 week for example. Then the log data will be emptied automatically."

2. WP keeps telling me I need to use a persistent object cache. My website provider is ovh.com. Not sure what more I can describe here...

3. A scan on semrush.com apparently indicates issues with 'mixed content'. This scan was done by a guy who will help me with google ads. He noticed this might be a reason why my ads don't get displayed. However I can't find any other indications of that issue.

4. "Page cache is detected but server response time is still slow". I have the Super Cache plugin installed, but WP is not entirely happy yet

5. "A scheduled event is late. The scheduled event, action_scheduler_run_queue, is late to run. Your site still works, but this may indicate that scheduling posts or automated updates may not work as intended." I had some cron-plugin installed but didn't get it solved with that.

6. I would like to have reCAPTCHA set up for my contact forms, but don't succeed. Something just doesn't want to go.