Kind of sounds like the tube needs to be replaced, but if it's just over a year old with light use that shouldn't be the case. Also, have you contacted Epilog? Even though you bought it second hand I would think they would still help you.
I've heard of people getting lines due to faulty safety switches that disable/enable the laser during cutting, but since you always have an issue right at the start I'm not sure that's the case, but then again it could be compound problems.
My best guess is that it's time to replace the tube but I would contact Epilog and see what they say. The good thing about buying a reputable brand like Epilog is the ability to contact them.
Here's a nice blog post showing the replacement of the tube, for your reference. https://www.evilmadscientist.com/2012/replacing-the-laser-tube/
Please post an answer here when you get it figured out to help other people that run across the same problem. If there's any other way I can help please let me know. Best of luck!