If I open a 32-bit TIFF file (either 32-bit unsigned integer or 32-bit float) and then export it as RGB 32-bit, the resulting file cannot be read by other applications.
The export was done as follows: File->Export->More then select file format as "TIFF" and Pixel format as "RGB 32-Bit"
The problem was found in Affinity Photo version 1.9.0.932
Update: I had compression switched on. If compression is set to "None" then the file can be read but if it is floating point then it displays incorrectly in the other application (e.g. PixInsight and Photoshop) as almost uniform grey. Perhaps the floating point numbers are being interpreted as integer because of an incorrect header.
Mark