Hi,
The problem is that, it will depends on the number of targeted elements.
How many product is there in your category ? (the mass action should give you this number).
If I test in my local website, with 10 products, it works but I guess that you should have many more and maybe some products with already variants.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.