HA started to respond very slowly

Hi,
can you point me to a guide, which would help me troubleshoot my HA installation?

About two weeks ago, I’ve setup HAOS on RPI4b/2GB with a few addons and it it worked fine until yesterday. Today, HA web interface started responding very slowly, sometimes even with "Unable to connect to Home Assistant. ".

I’ve not made any changes in HA configuration since yesterday, no updates. There is enough disk space available, 61 % used, 4.8GB free.

Thanks in advance for any help.