oxTrust has nothing to do with your case. If there are any clues, they will be in IDP and oxAuth logs. [Here](https://gluu.org/docs/gluu-server/4.2/operation/logs/#core-logs) you can find list of locations for all logs in Gluu.
It's hard to say why this delay happens. It can well be due to low performance of the machine you are running Gluu Server on (like if it's some cheap VPS with insufficient CPU allocations).
You could share HAR file of the flow with us, may be there will be a hint. You can use steps listed [here](https://www.inflectra.com/support/knowledgebase/kb254.aspx) - please use Firefox for that task, Chrome's HARs are flawed. Also don't forget to set "Persist log" and "Disable cache" checkboxes in the console to save everything, not just the recently loaded page.