RGBA to hex and backwards conversions have no losses except rounding errors, if the numbers are scaled. See for example Inkscape's coloring dialog (to use it you must have a dummy shape to be colored, I drew a rectangle):
Inkscape has scale 0...255 for R, G , B and Alpha. I had R=128, G=129, B=130, A=131. The hex version of those RGBA numbers is 80818283 as you should well know if you say you are a programmer.
Some software can have decimal RGBA numbers in scale 0....1 or 0...100% and the format can be mixed like it was in your example. If A=0.7 in one system, it should be 0.7*255 in Inkscape, but rounded to the nearest integer.The rounding error is the only error.
CMYK to RGB and backwards conversions aren't unique nor lossless, because often the numbers are used in different devices which have different color spaces (=different sets of possible colors).
In Inkscape and GIMP RGB and CMYK color spaces are assumed to be equal. Black ink (=K)is totally redundant, all possible RGB colors are possible with C, M and Y. K can be zero. One can increase K and keep the color still same by adjusting C, M and Y as long as the numbers can be 0....100%. That scaling is reflected from the meaning of those numbers in printing. They are percentages of max amount of ink that the paper can hold.
In CMYK printing aware software (not GIMP, Inkscape nor Microsoft Office) CMYK <-> RGB conversions are made by applying device color profiles. They are used either to show what the numbers will give or to give the same apparent color as exactly as possible in different devices for ex on the screen and printed onto paper.