Reminders app - random sorting

I'm having a similar issue. I have a perfectly manually sorted template with 72 items across 6 sections. When I make a new list from the template, for a minute they're correctly sorted. And then iCloud syncs (you can see the little icon flash) and the items in the sections get randomly sorted. It's still set to manual. Yes, it's list saved in iCloud. Not all my templates do this but I even tried fixing the sorting in the new list and then saving a new template from that...nope same problem. An older template with 90 items (but no sections) stays sorted just fine. It's so annoying.

I am having the exact same issue. Called Apple Support back in early November 2023 and told me they had no idea why it was doing this and "would add it to list of fixes". Major pain in the *** they can't fix this ASAP. It was working perfectly before.

You have not mentioned where your Reminders were stored, on iCloud or other email Accounts. Please see the pic below