OK, reproduced this error with 44428 on 20200625-6f685ae5d0-win_x86.

Not sure if this is the problem, but the author, truestone, was removed at some point, perhaps along with all his recipes, which were deemed a little too capable.

A comment from tamirh seems to indicate an error of the type noted would occur attempting to download a removed recipe. I get the same error on removed recipe 45935, so maybe it's working as designed, although not a great design.

Then, just for laughs, I tried downloading recipe 44429. Client crash after a "can't find recipe" message. While there's a little variability, in the original interface, the crash seems to hit on the second download error. In the selection interface, it seems to hit after the first error message is displayed. Sample log.txt and debug.txt attached.

A test or two later, it seems that all truestone's recipes got the treatment. Go to https://fold.it/portal/recipes?page=0%2C0%2C0%2C0%2C0%2C0%2C49&sort=asc&order=Player for other examples.