Since ios 18 Beta 4 my celluar connection is unstable. Dropping from full service to none at all. Or just showing Edge speed. Same issues with my eSim as well. Funny thing. Sometimes my eSim has full reception and my regular Sim none at all. Ok. no Internet services anyhow. Was not solved in the iOS 18 Beta 4 rerelase on Saturday.
Filed a feedback as FB14486702