Hello Abel Jashua Heredia Chavez,
>I'd like to find the root of the problem and fix it, but I don't even know where to begin.>>Any suggestion is welcome, thank you so much!
Would you know if slowness is in the responses from APIs or in publishing said APIs?
Otherwise, without any other info we recommend to take some latency logs to find out exactly where that latency is coming from.
Here are some links to help you with that:https://www.ibm.com/support/pages/analyzing-datapower-latency-loghttps://www.ibm.com/support/pages/troubleshooting-datapower-how-set-extended-latency-log-targethttps://www.ibm.com/docs/en/datapower-gateways/2018.4?topic=targets-latency-messages
If that slowness is due to the backend, the document cache, or parsing, the latency logs will tell you. If you don't know why the latency is showing in a specific action, if it's showing up everywhere, or intermittently then a support ticket is recommended to review the data.
One reason for the slowness could indicate an internal memory leak of some sort. Since 2018.4.1.6 there have been many memory leak fixes. If that is the case, then upgrading to a newer fix pack might solve the issue.
Either way, we advise you to open up a support case and to take multiple nbleak reports for some time interval to show what might be the cause.
Some information on how to set up nbleak can be found here: https://www.ibm.com/support/pages/mustgather-memory-growth-datapower-firmware