I have a strange issue that suddenly appeared on a stable system. I'm looking for some help in how to approach debugging this

I have a LAMP system that has been up for many months. Apache 2.0.64, perl 5.8.8

The system just started generating errors this evening. The error is:

Undefined subroutine &ModPerl::ROOT::ModPerl::RegistryBB::www_vhosts_w
+ineinsight_2ecom_wineinsight_listaction_2eajax_2empl::authenticate ca
+lled at /www/vhosts/wineinsight.com/wineinsight/listaction.ajax.mpl l
+ine 67.
 at
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listaction.ajax.mpl contains:

...
28 use yyauthenticate;
...
67 authenticate();
[download]

And yyauthenticate.pm contains the authenticate subroutine in an unnamed package (loads into main)

Again all has worked just fine with this code until this evening. The behavior is that some requests work, and some generate the error. I'm not certain if only some PIDs always generating the error and other PIDs always work. Restarting Apache doesn't change the behavior. Any ideas on how to approach this issue?

Some other info from the http.conf:

<Files ~ "\.mpl$">
    Header set Cache-Control "max-age=0, no-cache, must-revalidate"
    SetHandler perl-script
    PerlResponseHandler ModPerl::RegistryBB
    PerlOptions +ParseHeaders
    Options +ExecCGI
    Order deny,allow
</Files>
[download]

I have a startup.pl with the following

use ModPerl::RegistryBB ();
...
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