Although GSC says “no issues detected”, the drop in the number of indexed pages (30k to 19k, a loss of over 400) is likely due to the indexing of low-quality, duplicate, or low-priority pages by Google’s 2025 algorithm. Check GSC’s Page Indexation report, check URLs, audit content, fix duplicate content, optimize links, optimize crawl budget and monitor updates, and use free tools like GSC and KeySearch to adjust your budget.