V-carving issue

I ran a relatively deep V-carve toolpath, and got a line near the top. I did 4 numbers (a friend requested a plank with 2016 in comic sans because both deserve to be burnt in effigy), and each had the line shown in the picture [goo.gl]. I ran each number as a separate toolpath so I could shift the board each time. I had to abandon the first attempt due to a hold-down issue, and it happened there pre-issue as well. It's likely operator/hold-down error, but I thought I'd see if anyone might know specifically what'd cause it. Thanks!

That line is just an artifact from Vcarving deeper than the bit goes. You can either accept that that is going to happen and sand it out or get a bigger V bit.
One other thing you can do is set your max depth just shallower than the bits capacity. This will give a whole different look with flat bottoms but you can see if you like it in the preview after tweaking the settings.

Just as mark said - set a flat depth to your V-carve. If you are using solid wood - you usually don't want your carving too deep anyway or it can warp on you.

Also - if it drastically increases your cut time, use the large area clearance tool. It will require a bit change - but you will find it cuts much faster than V-bit alone.

However, in my personal experience, the more you can get away with a normal V-bit the better. A larger 90 degree bit may be the best option.

Ah, good to know! For this, we decided cutting as deep as possible was ok, since he wants it to burn as easily as possible. I will keep that in mind for future projects, thank you! This is the final result: [goo.gl]