Iphone 11pro, iOS 14.4, provider Vodafone UA. Issues with network too. I have installed 1 physical SIM and 1 eSIM in my phone. The issue occurs for the SIM card where cellular data (3G or 4G) is enabled. Issue happens periodically, can occurs several times per day. The signal bar can show 2-4 bars for related SIM, but it's not possible to receive or make calls, use mobile internet nor receive any text messages. If SIM has mobile data off - it's possible to make calls all the time. Rebooting helps. Switching on/off air plane mode - sometimes can help, but it requires 3-5 cycles of turning on/off. Manipulating with different cellular settings or resetting - doesn't help. Only switching off mobile data for related SIM helps.