I know paths on WIndows with Xampp is listed as a known issue, but we've had no problems with previous versions.

Since the last release we get an issue where the physical path and base URL are joined together to output invalid URLs for JS and CSS.

We managed to track it down and solve it by changing this:
Line number 254 in /includes/CMB2_Utils.php

Current:

$site_dir = ABSPATH;

Adjusted:

$site_dir = self::normalize_path(ABSPATH);

I'm not sure if this would have knock-on effects, but it seems to work without issues.

If it has no side-effects, can you please make the adjustment.