For something so thin, your soldering woes aren't surprising. The standard way to manage that would have been to solder everything in one go on a hot plate (reflow soldering).
Thank you,
My first few attempts were with a SMD stencil and a 50x50mm hotplate, it's true that maybe a larger hotplate that could span the whole PCB might have done a better job. But with the smaller plate it was "easier" to just manually apply solder paste and do 4 switches at a time.
I think this method is also highly specific to these switches. They are known for being difficult to solder with hobby-tier equipment.
For something so thin, your soldering woes aren't surprising. The standard way to manage that would have been to solder everything in one go on a hot plate (reflow soldering).
https://www.youtube.com/watch?v=QarizoUnRfk