intermittent home-page 404

I’ve been chasing an intermittent home-page 404 on a dev site and it traces back to LearnPress, so I wanted to flag it with what I found.

Every so often the site’s home page (/) returns a 404. Flushing permalinks clears it straight away, but it comes back on its own after a while, and it only happens with LearnPress active. Deactivating LearnPress stops it completely.

The cause is that LearnPress hooks option_rewrite_rules at priority 1 and array_merges its own ruleset into the option every time it’s read (LP_Query, from what I traced). Filtering that option is a known WordPress core gotcha (Trac #37561): flush_rules() reads it while regenerating the rules, so LearnPress’s merge feeds back into the regeneration. In that churn, core’s $ root rule (the '$' => 'index.php?' that routes / to the front page) gets pushed out and never makes it into the saved set. With nothing matching /, the home page 404s. It keeps returning because every regeneration (a plugin activating, a permalink save, an update, core’s own self-heal) is another chance for the rule to drop.

Digging in further, LearnPress re-injects its whole course/profile/checkout ruleset into extra_rules_top on every request, and the per-request guard that should stop it doing that repeatedly looks like it’s commented out in the source.

To reproduce: static front page, permalinks on /%postname%/, LearnPress active. Save Permalinks (or activate any plugin) to force a regeneration, then check the stored rewrite_rules option and you’ll see the $ rule is intermittently gone, with / 404ing when it is.

I think the fix is to register LearnPress’s rewrite rules the standard way, at generation time via add_rewrite_rule() or the rewrite_rules_array filter, rather than filtering the stored option on read, and to re-enable the per-request guard so the ruleset isn’t merged in every request. That keeps LearnPress clear of flush_rules() and lets core’s root rule survive.

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