You are today not the first one with this issue.
Seems like some UPDATES were done related to the functionality of dropdowns.
@yisrael-wix Perhaps you should take a look on this issue (it is not the first today related to dropdowns).
What you can try to do is —> delete the dropdown completely and add it again. Check if it got back it’s functionality.
https://www.wix.com/velo/forum/community-discussion/editor-bug-selectors-no-longer-valid
https://www.wix.com/velo/forum/community-discussion/unable-to-select-one-specific-element-code
Thank you for the fast reply!
Unfortunately after trying everything from my end, nothing helps. Every new dropdown reporting the same error.
I am afraid this will affect the live site and don’t want to publish any changes.
Hoping for the solution from the WIX team side 
@yisrael-wix
Hi everyone,
Thank you for letting us know about this issue. We’re currently investigating. Apologies for the inconvenience.
This issue is now resolved. Please let us know if you continue to have any problems. Thanks!