How to fix this problem: poor performance and server / site instability (404 and 504 errors)

Hello guys! I have a website (tobruxo.com.br 1) and I am suffering from instability and performance problems and this is really hindering my rankings on Google.

I started having these problems after I published more than 10,000 posts, before that there was no performance or instability problem.

All of these posts were published via API but I don’t think this is related, my server is hosted on Digitalocean, follow the server specifications:

• 8 GB RAM
• 4 CPUs (Shared)
• 160 GB SSD Disk
• 5 TB Transfer

The errors I’m getting are usually: 504, 404

Detail this is an AMP page that exists, but problems occur on all pages and not only on AMP pages.

Can anyone help me with this performance issue? I’ll leave a log below that I got from the server with the ghost log command:

        [2020-10-26 22:47:50] INFO "GET /anime/especial/shingata-jii-5-daime-lt-am-3501/" 200 30368ms
        [2020-10-26 22:47:51] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 20224ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.tagsPublic.browse","apiOptions":{"order":"count.posts desc","include":"count.posts","limit":"4"},"returnedRows":4}


        [2020-10-26 22:47:51] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 24190ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.postsPublic.browse","apiOptions":{"filter":"id:-5f94cf9076e31f0862c4457f+tag:ova","limit":"3","include":"tags,authors"},"returnedRows":3}


        [2020-10-26 22:47:52] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 21209ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.tagsPublic.browse","apiOptions":{"order":"count.posts desc","include":"count.posts","limit":"8"},"returnedRows":8}


        [2020-10-26 22:47:55] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 23532ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.tagsPublic.browse","apiOptions":{"order":"count.posts desc","include":"count.posts","limit":"6"},"returnedRows":6}


        [2020-10-26 22:47:56] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 25011ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.tagsPublic.browse","apiOptions":{"order":"count.posts desc","include":"count.posts","limit":"8"},"returnedRows":8}


        [2020-10-26 22:47:56] INFO "GET /anime/serie/ni-ga-mushi-ojisan/" 200 29558ms
        [2020-10-26 22:47:58] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 27032ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.tagsPublic.browse","apiOptions":{"order":"count.posts desc","include":"count.posts","limit":"6"},"returnedRows":6}


        [2020-10-26 22:47:59] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 29257ms to complete

        level: normal

        ERROR DETAILS:
            {"api":"v3.postsPublic.browse","apiOptions":{"filter":"id:-5f94fa3176e31f0862c48559+tag:especial","limit":"3","include":"tags,authors"},"returnedRows":3}


        [2020-10-26 22:47:59] INFO "GET /animes-acao/amp/" 304 22261ms
        [2020-10-26 22:47:59] INFO "GET /content/images/2020/10/ane-wa-yanmama-junyuu-chuu-1.jpg" 200 4ms
        [2020-10-26 22:48:00] WARN

        NAME: HelperWarning
        CODE: SLOW_GET_HELPER
        MESSAGE: {{#get}} helper took 28453ms to complete

        level: normal

Below is the Ghost version:

Ghost-CLI: 1.14.1

Ghost: 3.36.0

Can anyone help me with this problem?