Sorry, I do not see an issue. Tested in 5.1.10. and 3.27.17
Try to clear your caches (browser, assets)

Anyway you could try to hardcode. Instead of {{ gT("First name:") }} only Login:

BTW: I do not see a registration form in your survey.

Thank you Mr. Joffm very much! 
Your post pointed me on right path! Everything work perfectly!
I made mistake - I edited register_form.twig and expected changes in resume_later form...

For others greenhorns (like me) - "resume later" screen you can edit in save.twig.

THX!
Pawel