is-sticky is not being added despite being sticky, if scrolling down fast

[simplenotezy]

Describe the bug
The 'is-sticky' class is not being added, despite the "position:sticky" is being added by stickybits. I can trigger the error if I scroll down a page very fast - it some times takes a few tries before it happens though).

See this video.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://thejewelleryroom.com/jewellery
2. Scroll down very fast (try CMD+ARROW DOWN on mac, or perhaps CTRL+ARROW DOWN on windows, to go to bottom of page)
3. The stuck bar will be stuck, but is missing "is-sticky" class.

Expected behavior
Should receive "is-sticky" whenever position:sticky is set on the object.

Screenshots
See video:

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Config

stickybits(this.$refs.productListHeader, {
	useStickyClasses: true,
	stickyClass: 'is-sticky',
	stuckClass: 'is-sticky',
	stickyBitStickyOffset: (this.$isMobile()) ? 61 : 144
});