SharePoint Search Index Journal file occupied 400GB space

We have SharePoint 2013 on premises with two search servers and search items are 20 Million. Server 1 with primary index component is running fine and server 2 with index replica component got degraded. When checked for search status, it showing ‘index out of sync and catching up’ but it is running for more than 36 hours.

After checked the Journal file, it occupied 400 GB space it is continuously occupying more data and utilizing all disk space.

What could be the issue and how to resolve this