Element disappears (inconsistently) after hover on animation

I’ve created a mouse over interaction to make the bottom line of links in tabs grow left to right. The problem is that sometimes — and quite inconsistently — the “line” (it’s actually a div) disappears after the hover-in animation. I cannot understand where the problem is. I don’t know if it’s a bug from Webflow, or something I can fix. Thanks!

You can find the live example here: http://preview-5fb031.webflow.io/
Webflow preview link here: https://preview.webflow.com/preview/preview-5fb031?preview=401cc889e02c8a61fa53334514c1d7ee