The post I’ve linked to in my previous one was a clear instruction how to find out what the new Windows10 client requires and which of its requirements are not compatible with your current settings.
Instead of following that instruction to find out how to slightly modify the current L2TP/IPsec setup, you have tried with another VPN mode (ike2) at Windows side. But the requirements for phase 1 and/or phase 2 authentication, encryption, and other algorithms exist in ike2 case as well, so without finding out which combinations of these algorithms the client supports and proposes, you cannot succeed either.
So without visualizing the failed communication, there is no way ahead.
So I’d keep the configuration on Mikrotik side in its working state, double-check that by connecting one of the “old” PCs which do connect successfully, and then disconnect as much IPsec peers as you can without affecting your workflow (to minimize the amount of unrelated events in the log), start the logging and press [connect] on one of those Windows10 machines which fail to connect. After getting the error message from Windows, you can stop logging and start reading the log. It is not that hard but if you feel lost, just obfuscate the IP addresses and post the log file.
And one general remark - L2TP/IPsec doesn’t work for two clients accessing the same server from behind the same public address unless you implement a server-side workaround.