Cylinder one misfire on cold start

Hello. I have always taken good care of it. It sat for a few months from about February-July. During that time, my husband would occasionally start it, but it was not driven during that time. I started driving it again a few weeks ago. It was not running right, and I took it to my mechanic and spent about $1,000.00 to get it running properly. The day after I picked it up, I noticed the yellow engine light flashed when I started it, but then went off. I wasn't concerned since it went off. The next day when I started it, the yellow engine light stayed on. I drove it about 50 miles-some highway, some city. It was driving fine, I didn't notice anything different than usual. I took it to AutoZone and they ran a diagnostic test and the only code that came up was p0301 (cylinder 1 misfire). They recommended changing the ignition coil for cylinder 1. I spoke to my mechanic and he agreed. He also recommended changing the spark plug for cylinder 1. So last night my husband changed the ignition coil for cylinder 1 and all the spark plugs. He also has a tool for checking diagnostic codes and we used it to reset the computer. We drove the car for about 5 minutes and had no issues, no lights came on. The next day I started it and the yellow engine light flashed for a few seconds then went off. I let it run a couple minutes then turned it off and turned it back on. That time, no lights flashed. I waited a few hours and started it. Again, yellow engine light flashed about 15 seconds then stopped. I drove for about 15 miles and it drove fine. Nothing felt off. Turned it off and turned back on, light didn't flash. So it seems to only happen on cold start.