I have the exact same one. I've found the location of the incubator in the house to be very important. I tried the basement, steady but too cold. Kitchen was too drafty. Bathroom was drafty and too cold. Now I have it on the corner of the dining table, into the corner of a room, well away from air currents or drafts of any kind. It went from crazy readings to rock solid operation like I'm used to.
I also put a bath towel around the side that faces the room, to protect the back end from any drafts. I left a little path between the wall and the table so that I can get to it.
Seriously though, I tried every spot in this house that had access to power. My last resort was to set it up inside a wooden box to protect it from these drafty windows. I don't start replacing parts until I rule out environment. It's supposed to have a room temperature of 70-ish degrees for the best operation, but in the winter, we're at 60-62. So I tried every location I could, 3 days in one spot to check, before sticking eggs in.
At my dad's house, I had the same type of incubator. In January, it was so cold and drafty, no spot in the house safe. I had the whole incubator covered in towels with only a bit of the top exposed so that I could still check it.
I first noticed the issue when ever the heat kicked on, I got a spike. When it was off and the air changed, I got a dip. Up and down, up and down. Until I switched it to the spot that had the most "dead" air.
