My apologies for the delay.

I logged in and had a look.

You have many plugins installed. It is very likely there is a 3rd party plugin which is causing a conflict.

There are 2 thins you can do,

1. Switch to the default Twenty Seventeen theme to see if the problem is present there, then just switch back.

2. Disable plugins until the issue goes away to identify the plugin causing the conflict.

3. Update all your plugins to make sure they are using the latest version.

Let me know if this helps.