Theme Settings page, dropdown fields not working

We are using Roots Starter Theme version 7.0.1 (there is no option to update).

When our WordPress updated to version 5.0+, we encountered an error with our Theme Settings page. This error occurs for all versions later than 5.0 as well.

Several of the fields on this page are dropdowns.

Prior to the upgrade, these dropdowns allowed for us to choose from a list of items.
After the upgrade, these dropdowns only allow for one item to be chosen (the current item).

Screenshots can be found here:
Before upgrade.
After upgrade.

How can we rectify this?

We don’t really have any way of knowing how your original developer might have implemented this feature. I’d recommend contacting the original developer if you can. If that’s not possible then you might post in our jobs section to hire someone to fix it: jobs - Roots Discourse