I had the same issue but when I took my phone to the sprint store I found out that if you pre-ordered the phones it didn't come with the network card (Sim card) and if you are using the network card from your previous device you will have these issues. So they swooped out my S10+ and they put in the correct network card because I was using the one from my S8+ and every since then I have not had anymore issues. I was told of your using the old network card you will have these issues and they are unsure to why the pre-ordered phones didn't come with the network card.
I then told them that they are going to have a lot of customer complaints due to this foolishness.
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