Google Took too long to crawl and index new contents (Used to be very quick)

For the past 4 months I start to noticed that Google took way too long to index my new contents, back then (2020) It used to be instant (longest it took was 1 day).

However since my website ran into problem on October last year (problem was Too many visitors, website crashed and we have to buy more server storage). The crawl and indexed behaviors start to changed.

Instead of taking longest (1 day) to crawl and index the result, the index period took longer (2 to 3 sometime even 5 days) and even if it indexed, my new contents ain't rank the same like before.

• Ranking factor (2020 prior to October) (#1 to #5 hardly reached page 2 of google).
• Ranking factor (After October to now) (Google Page 2 - 5, sometime can't even find the contents).

Also worth mentioning my website contents are about game guide so we build up a huge fanbase, that is why I didn't noticed the problem instantly.

Question: What caused it? I am 100% sure that my contents is not a factor. How can I fix it? My developer tried to and they still try to figure out, but the problem seem beyond removing useless script and such. Any help is highly appreciated.