This doesn't sound right, so we should take a closer look at the order(s) in question. Can you make a support request (https://support.kraken.com/hc/requests/new) and include the numbers of the order(s) that seemed to be skipped? The order numbers can be found in the left column under Trade > Orders in your account (only the first 6 digits of the order number are shown and you have to click to get the full number).
Ok, will do
edit:
Looks like the order finally completed at some point....good job I noticed before filling out support request
Yes, market orders match instantly against opposing orders on the book. There's no such thing as "the" market value. The average price you pay depends on your order size and on what orders are on the book to fill it. For example, suppose you sell 2 BTC at market and the highest buy order on the book is 1 BTC for 211 and the next highest buy order is 2 BTC for 210. Then your 2 BTC market order will get 1/2 filled by the order at 211 and the rest will get filled at 210. Then your average fill price on the sell order will be 210.5. In this case if you go to look at your trade history, you will actually see two trades (one at 211 and one at 210), since it took two trades with two different orders on the other side to fill your order.
Thanks also for the explanation.