Comment 1 for bug 1268896

The problem arises when ultisnips tries to unmap select mode mappings for printable characters. If vim-airline (or you in you .vimrc) is mapping something using :vmap you should probably open a bug report with them telling them to NEVER use :vmap, but always :xmap (see help mapmode-x):

NOTE: Mapping a printable character in Select mode may confuse the user. It's
better to explicitly use :xmap and :smap for printable characters. Or use
:sunmap after defining the mapping.

You can work around your problem, see UltiSnips-warning-smappings.

I can see that this is still a bug in UltiSnips/Vim - somehow the mapped characters are not really printable/decodable the way we get them from Vim - I guess you are using a non ASCII mapping someplace. However, I have no idea how to fix this - I think the problem is that Vim is not reporting the mappings correctly while listing them. Let me know if the work around works for you.