Hi,
You have the same issue with some products.
I think that your website do not have the right to create thumbnails anymore ; it should be something related to the write access for the folder "/media/com_hikashop/upload/thumbnails/" or just the "/media/com_hikashop/upload/thumbnails/50x50fsO" one.
But if you have the issue also in the front-end ; more folder thumbnails could be involved.
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.