FYI...manually scanning the wp db identified my 2 errors
Table = wp_postmeta
Field = meta_key = _aphs_FYN_postcode
I found one PCode value with no space (CDN pcode is A9A 9A9) it was entered as A9A9A9
The second had a space as first character (eg. <space>A9A 9A9)
In both these cases, the php function would be looking for a numeric value at a certain position but read an alpha character instead. Hence the php error "expected parameter to be double, string given" (in plain eng, 'expected to see a number, but saw a letter instead)
Manually correcting both these records removed the Warning error.
Hope this helps...Rob