thanks for your reply. I've read the wiki and checked the forum before. But couldn't find something similar to this.
In our wiki, we don't mention that Buster is supported, and if you look at the INSTALL.md file of the latest stable version, you can see that the list of supported Debian versions are Debian Jessie (7.x) and Debian Stretch (8.x). See https://github.com/i-MSCP/imsc…supported-debian-versions
So, basically put, you're using an i-MSCP version, and a PhpSwitcher plugin version that were not tested under Debian Buster. Current i-MSCP stable version is compatible with Debian Stretch, not with Debian Buster. Therefore, I'm primarly wondering why you did that update without more thinking about your current environment... Debian Buster has just been released.
Regarding the configuration failure when you try to re-compile your PHP versions, this can be due to many things... I cannot say more without investigating directly on your server.