Check this
KV store troubleshooting tools - Splunk Documentation
Hi @Dikshi
Please could you check your splunkd.log for any errors relating to Mongo/KVStore and report back.
Also - Have you made any changes recently to either Splunk version, permissions, certificates or operating system?
Please let me know how you get on and consider accepting this answer or adding karma this answer if it has helped.
Regards
Will