I recently saw a great YT video on Google Search, it explains how vast the internet has become recently especially in relation to the mass over population of spammy content from naughty seo activity.
User generated Community content used to organically rank really well in Google. But I suspect that in the process of Google dealing with all this spammy content, they have indirectly impacted sites that generate new content daily.
We've found using Google Search Console Tools is a good way check up on any issues with crawling - best follow Google's own guides on this
