I doubt it has anything to do with a + character, more likely it's to do with the fact that .* is greedy and you've got two links on the same line, as Corion said.

Yes, I realize that Perl regex is not the way to go to find links.

Correct! Sorry, but in regards to "my method works": it's not really working, though. And even if you fix this one issue with this one input, the next problem will certainly pop up - see this node for how complex parsing HTML gets*. In this case, there's a very well established module for that, HTML::LinkExtor. Mojo::DOM also works:

use Mojo::DOM;
my $dom = Mojo::DOM->new(<<'END_HTML');
<a href="https://www.example.com/foodbanks/a">a</a> <a href="https://w
+ww.example.com/foodbanks/b">b</a>
<a href="https://www.example.com/foodbanks/c">c</a>
END_HTML
$dom->find('a[href]')->each(sub {
    print "$_ / ",$_->{href}," / ",$_->all_text,"\n";
});
[download]

Edited second paragraph.

* Update: Why a regex *really* isn't good enough for HTML and XML, even for "simple" tasks