The SMT cold solder joint rate suddenly increased today. Should I check the reflow oven temperature or the solder paste condition first?

After switching to a small-batch board on the SMT line today, the AOI reported an increased rate of false cold solder joints. The reflow profile was just verified last night, so I didn't change it immediately. Instead, I first checked the solder paste opening time, thawing records, stencil cleaning frequency, and placement pressure. It turned out that because this batch of boards was waiting for…