Cause of glitches with Let's Encrypt certificates?

Question

Apache HTTP Server

Tell me, does anyone have a dance with Lets Encrypt certificates? I used it normally for two years, now for the last two months it opens every other time: either a normal certificate, or the browser writes "invalid". Refreshed the page several times and it's fine again. Errors come from Yandex and Google spiders on the same topic, respectively, problems with indexing sites have begun.

Tell me where to dig? There was some story with the IP Lets Encrypt block, is this problem relevant? Own server, Ubuntu/Apache. All certificates are updated, the certbot renew command writes about all domains not due for renewal.