There are two ways you can approach this.

1. you can reverse the order of the activity stream. This will move the Details to the top and show the comments in the reverse order that they currently show.

2. you can move the Details to the top and leave the comments in the order they currently show.

Both of these will require you to edit CSS. There are several add-ons out there that will let you do this, but I recommend Scriptrunner (as that add-on provides so many other useful functions as well). The following two CSS are for the above options:

Option 1:

.vp-activity-list.insight-init {
display: flex;
list-style: none;
flex-direction: column-reverse;
} 

Option 2:

.vp-activity-list.insight-init {
display: flex;
list-style: none;
flex-direction: column;
}

.vp-activity-list>li {
margin: 0;
padding: 0;
order: -1;
}

Under the new view in the Cloud version, changing jira.issue.actions.order under Advanced Settings does not seem to work. Neither logging off/back on nor rebooting my machine has an effect. 

Can this be fixed please?

In the Service Desk Portal, when a customer reads the history of an issue. The issue summary is shown at the BOTTOM of the page. However, for service desk agents, this information is at the TOP of the page.

For Service Desk Agents. The Issue Summary and Issue Description are critical information for understanding and responding to the issue.

For Customers. The last comment is first and foremost on the Issue page and so becomes the focus of their response.

As a result, there is a clear disconnect in the conversation between Customers and Service Desk Agents. Both have a distinctly different focus.

I would like to change our Service Desk Portal such that:
1. The Issue Summary details is ALWAYS at the top of the Issue page for customers. So that they can see and review the original request details, each time they respond.
2. That comments are sorted in the SAME order as Service Desk Agents see, by default in JIRA.

These two simple changes would greatly enhance the overall experience of our customers, increase the effectiveness of our support team and reduce the support work load by keep support requests on TOPIC.

Related change requests: JSDSERVER-507 and JSDSERVER-190

I'm very interested in getting this issue FIXED.

Provide our customers with the ability to at least quickly sort the comments dynamically. Rather than have a fixed listing.

We find ourselves having to repeat the same comment to customers because they cannot scroll down far enough or reverse the sort quickly.

This is reminiscent of the top-posting vs bottom-posting wars of days yore (Usenet, email). Some people prefer the ascending order. Some - the descending order. Because many a flamewar has been fought over this sort of a thing, perhaps having this configurable per-customer account is the answer?

Unlike the Usenet or email, the content in the Customer Service Portal is dynamically rendered, and the individual comments are held in a database, which lends itself to being a configurable setting.

Something similar to this is already done, in fact. jira.issue.actions.order under Advanced Settings changes the sorting of how the actions for a given issue are displayed. Documented, helpfully, here A global setting, but the code already exists.