I can't remember exactly when this happened, but for the past couple of days, all sdlxliff files on my computer are displaying a MemoQ icon instead of the actual Trados Studio one.
If you've encountered the same inconvenience with this file type or any other, here's how to fix it.
File type associations
1. On the Windows File Explorer, right click on any of the problem files and select Properties, then click the Change button on the Properties dialog box.