(Screenshot upper half there is a diff between unpatched file (left) vs patched file; whereas lower half of screen shows patch, as ensues below)

Had seen a few of those 500s in error.log file(s).
Began to investigate the issue and subsequently...

---
 inc/sessions/model/_hit.class.php | 1 +
 1 file changed, 1 insertion(+)

diff --git a/inc/sessions/model/_hit.class.php b/inc/sessions/model/_hit.class.php
index 15dd57517..0eca58d7d 100644
--- a/inc/sessions/model/_hit.class.php
+++ b/inc/sessions/model/_hit.class.php
@@ -465,6 +465,7 @@ class Hit

                        if( $Settings->get( 'antispam_block_spam_referers' ) )
                        { // In order to preserve server resources, we're going to stop processing immediatly (no logging)!!
+                              load_funcs( 'skins/_skin.funcs.php' );
                                siteskin_init();
                                siteskin_include( '_403_referer_spam.main.php' ); // error
                                exit( 0 ); // just in case.
--
2.30.2

line of code:

load_funcs( 'skins/_skin.funcs.php' );

is missing in

b2evolution/inc/sessions/model/_hit.class.php

and will cause a 500 error. The above patch will fix it.