Affinity is not able to open SVG files with a special syntax where some whitespaces are missing.
This syntax follows the standard SVG 1.1 so is expected that Affinity is able to read.
In the attached example an arc is wrote as:
a.65.65 0 011.109-.459
The string 011.109 contains 3 values:
1 (a boolean is required here, it cannot be 11.109)
This syntax (with missing whitespaces) follows the SVG 1.1 standard: https://www.w3.org/TR/SVG11/paths.html#PathDataBNF
The example is properly displayed on Chrome and Firefox.
This issue has been discovered using SVGO (https://github.com/svg/svgo/issues/1137)