I have a Viking (2 ovens) range. I had to replace the igniters to get it to work right. There is a small oven with one igniter and the larger oven has 2. The stock igniters from Viking are junk. I found some better aftermarket igniters several year ago and haven't had an issue since. I wish I could remember the brand, but since product recommendations are considered off topic, it's probably best I can't remember the brand. Just don't get Viking brand replacement igniters.
OK....down to the details on how this works. The igniters are connected to the fuel valve, they need to draw enough current to "convince" the fuel valve they are operating correctly and will indeed be hot enough to ignite the gas when the gas valve opens. If the igniters don't draw enough current, the fuel valve either won't open or close if the current drops too low. The igniters on Vikings run contentiously when the burners are operating, so if they draw less current, the fuel valves may shut down.
I think it's a crummy design and would much rather see a flame sensor or ignition proving device like are in gas furnaces. Oh well, Viking didn't ask me first! Hope this post helps. If you want the brand of the replacement igniters, let me know and if I can find it, I'll post it in a comment.