The quantity in the product is always unlimited after saving

Hello,

We tried it here on the same versions, on a simple product and on a product with variants, and the quantity saves and stays. So something on your site is writing the value back after the save.

Two things you can check yourself before we go further :

1) HikaSerial. In its configuration, under "Advanced settings", there is a "Link product quantity" option. When it is on, HikaSerial owns the stock of every product attached to a serial pack: it recalculates it from the free serials of the pack after each product save and after each order, and a pack that generates its serials, or that has its unlimited quantity option turned on, gives "unlimited".

2) Mass actions. Go to System > Mass actions and look for one that changes the quantity of your products. A mass action can be set to run on a schedule with the cron, so it would reset the quantity of all your products on its own and undo your change shortly after you make it, or it could also run after a product update to force back the quantity.

Either of those would explain both things you see, all your products switching to unlimited at once and the value going back to unlimited after you save one.

If the HikaSerial option is set to No and there is no such mass action, then it is something else and we would need to look at the site itself. In that case, send us a backend access through the contact form of our website and we will check it directly.