If pizza was heated up in a meat oven that had not been used in the past 24 hours, are there any issues?
Thank you very much.
If it was placed on a clean rack or a piece of tin foil etc. the pizza is not affected. If it was placed on a dirty rack that had meaty remnants the pizza should be discarded.
Concerning covered foods of meat and milk in the same oven, see Shulchan Aruch, YD 108:1; Ksav Sofer 54; Igros Moshe YD 3:10; concerning dry [even open] foods, see Igros Moshe YD 1:40 (and 1:59, concerning baking a challah) based on Pischei Teshuvah 92:6.