In magento 2 when save a category it taking long time and after that giving 503 error as below. This category have 12428 products. All others category save working fine. Only issue with this category.
Service Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later. Additionally, a 503 Service Unavailable error was encountered while trying to use an ErrorDocument to handle the request.
memory_limit - 4096M
max_input_vars - 4000
max_execution_time - 3600
MAGE_MODE - production
Indexing - Disable
Please suggest how to resolve this issue.
Thanks