Rae from Shopify here. Thanks for reaching out with this question about the slideshow on your Debut theme.
When did you first notice that the slideshow stopped transitioning automatically? Have you recently made any coding changes to your theme that may have impacted this?
As a first step to resolving this, I'd like to check your theme settings to ensure the slideshow is still set up to transition between slides. To do this, login to your Shopify admin, click on 'Online store > Themes' , and select 'Customize' beside your Debut theme. This will open up the Theme Editor. From this screen, select 'Slideshow' from the lefthand menu. Inside this section, under 'Settings', please check to make sure that the 'Auto-rotate slides' option is ticked, and the slider is adjusted to determine how many seconds each slide will display for. The settings should look similar to this:
Once the settings look like this, make sure to click 'Save' in the top righthand corner. Does the slideshow start moving automatically once you've ensured these settings are in place?
Please keep me posted on this and I'll be glad to help further!