It sounds like you misunderstand how to add rewrite rules as your structure is relatively common and should not require flushing the rules on every page load. The impact depends on your set of rewrite rules, and the codex is somewhat outdated and I don’t think it is as bad as it used to be … Read more
add_rewrite Rule
I found same problem and I solved with extraordinary article of Brent Shepherd : Advanced Taxonomy Queries with Pretty URLs. This article contains a generic function to solved the problem and instructions for changes permalinks. It’s very important don’t forget enable module php: mod_rewrite in your server and modify the archive /etc/apache2/sites-available/000-default.conf with rules: (for … Read more
The old permalinks still work because the rewrite rules that support those permalinks still exist. When you register a post type, setting the rewrite argument generates the rules to resolve incoming requests. Rather than adding new rules in addition to the originals, just alter the original post type registration.
Rewrite for custom type and custom taxonomy
properties_add_rewrite_rules should be hooked to init so it runs on every request. Rules can be flushed at any time- loading the permalinks settings page calls flush_rewrite_rules, and your rules weren’t added on that request, so they disappear.
Changing default slug of post to the post id
Intermittent Rewrite Problems
How can I map a specific URL pattern to a plugin for processing
Added incorrect rewrite rule now getting an error