Not all variations in WooCommerce are working

Firstly, all my plugins are up to date & WordPress is up to date etc..

I am busy building a website for our company, and some of the products have hundreds of variations.

Everything worked fine, but a few days ago I noticed that not all the variations work.

I load the product attributes, and then i use the “link all variations” button to link all the variations (50 at a time). When this is done, i use the bulk edit feature to set the prices, which is “1” (we wont display prices & i have disabled prices from showing).

Then i update, then when i go look at the product page, most of the variations work, but some don’t.

I have manually added the variations that don’t work, no luck. I have also recreated the page, only to discover that it doing this on previous products that i have loaded.

The error message i receive is:
Sorry, this product is unavailable. Please choose a different combination.

I have also spent the last 3 days reading through previous forums and cannot find someone with the same problem.

I am currently using an under construction page while i am busy capturing our entire catalog (this has taken me roughly 3 months to date), so i need to provide login details to who ever will be able to assist.

I really hope someone can help, because i am dreading having to redo this entire website.