My Spider IV 75 amp starting doing this about 6 months ago, does not make a difference if i use the shortboard or not.
Today, the amp went off and has not come back on, the amp sounds good when it works, but I will not get another Line 6 product,
they are not built with quality parts, cheap china lollipop to keep the cost down.
My warranty has expired, and the amp is designed to last about the same as the warranty, now you have a $300 paperweight.
The amp has never left my house, has never been mistreated, it is in mint condition, minus the thing not working.
If they are going to make a disposable amp, they need to drop the price down a bit more.
And yes, i'm a little more than pissed at this moment.... Sorry for the rant.