I discovered Samsung Automatic Data Switching a while ago and enabled it. If it will work for your setup I suggest you do the same.

When my primary SIM (Vodafone) has no network my phone automatically uses my 2nd SIM (Skinny) for data including WiFi Calling for SIM 1.

https://r2.community.samsung.com/t5/Tech-Talk/Auto-Data-Switching-on-coverage-and-reachability-issues-gone/td-p/11152369