Hi,
I see that you are using HikaMarket so I think that you do not have holes in your order numbers but you have vendor sub-sales that you're not displaying in your HikaShop order listing.
When HikaMarket creates a sub-sales for a vendor, it add an entry in the HikaShop orders ; so it increments the "order id".
So the ordering is still working ; it is just that you do not display the sub sales.
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.