Update for macOS and iOS:
By the way, some have suggested that 44.1kHz is all you need for correct audio reproduction and that is true, but it's only true if the audio file has been produced and mastered at 44.1kHz.
If there is any resampling in the pipeline, then the end product will necessarily differ from what it was in the producer's DAW (added distortion/artifacts).
The quality of the resampling might vary depending on which algorithm was used and whether or not the resampling was done by Spotify or before sending the master to Spotify, but any resampling will introduce "loss" of some kind.
Are these resampling artifacts audible? Most certainly not. But then again, I can't tell the difference between compressed and lossless anyway.
But are these new Spotify files lossless? That's only if they were at 44.1kHz before being sent to Spotify, and they are only lossless when compared to the sent file. When compared to the original project in the producer's DAW, then the sent file is only lossless if the project was at 44.1kHz to start with (not many producers work with 44.1kHz projects...).
In that sense, using the word "lossless" is misleading marketing.