Thank you for your message, I would be happy to help out. However, I cannot replicate the issue you are having when visiting the desktop version of your shop. I can access your navigation menus perfectly fine as shown here:
Is there a specific action you are taking that causes the menus to vanish that you noticed, If so, can you share that clarification with me? If you are still having this trouble, can you try clearing your browser history/cookies and cache and refreshing your page, or try an incognito/private window?
Please feel free to reach back out to me hear with your results if you are still having this issue, I would be happy to take a closer look!
Marty, thank you for the quick response. Apologies, I used the wrong term. I meant the hamburger button. When I click it the menu options appear for a few seconds and then disappear. As you suggested I tried clearing the browser history/cookies, cache and incognito as well and still having the issue. Thank you
My mistake, thank you for clarifying that for me! A good way to test if an issue is theme-specific is to test an unpublished Shopify theme to see if the issue replicates. You can do this by heading to Online store>Themes>Free Themes>Explore free themes and selecting a fresh Shopify theme. Once you select a new them you can test it by click Action>Preview:
If the issue does not replicate on the unpublished theme, this points to a specific issue with your primary theme. How did you create your hamburger menu, are you utilizing a third-party application or have you implemented any third-party coding to achieve this? If you are using an app, I would recommend reaching out to the app developer to take a closer look into this with you. If you manipulated your coding in any way, this is not something our theme's team would be able to support, however, one of our friendly community members may be able to take a look. Alternatively, you could always reach out to a Shopify Expert to take a closer look.
I hope this information gets you in the right direction, please feel free to reach back out here if you have any further questions at all!
This is an accepted solution.
Please add below code in bottom of assets/theme.css file