I’m unable to find the Gecko theme. Was this a third-party theme? If it was purchased through the Shopify theme store, or a free theme it should be fairly easy to troubleshoot.
Third-party themes that aren’t built by Shopify or our partners are hard to troubleshoot as generally, the partner will code customizations that tend to break as the platform updates.
Do you remember/ still have contact with the team, or site you purchased the theme from? If you can get in touch with them, they should have an updated theme version that would adjust to any updates with Shopify hopefully.
Can you try giving the theme developer a message and let them know about this issue? Hopefully, this is something they’re aware of it and it will just be a simple fix.