On shortish distance WSPR , especially on 6m and shorter wavelengths, Doppler shift from aircraft is a real issue: signals arrive directly and reflected off aircraft and sometimes WSPR cannot decode (often quite strong) signals. G0LRD has been analysing my signals and believes these have been frequently reflected off planes around Stansted Airport.
I have also seen large Doppler shifts on some trans-equatorial 10m signals and wonder if this is spread-F , moving F layers either side of the equator? Sometimes it is kit warming up, but I quite often see large Doppler on TEP signals and also signals crossing auroral (polar) paths.
On 6m and 2m, Doppler can make some VHF paths inter-G almost unworkable - strong signals but too much Doppler for the software to cope.