I started having this same problem last night and nothing I have tried on my own has resolved the issue. I finally resorted to calling my phone carrier. They initiated a network refresh on their end and advised me to give the phone 2 minutes to rest before restarting. In the meantime, I realized that I had just installed Samsung Flow on my phone to link it with my Tab S3 which is when the problems began. I uninstalled that as well. After the network refresh and uninstalling flow things seem to be working smoothly again.
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