Hi @Pawan Kumar,
Thank you for posting in this community.
1.If you have integrated and configured a specific malware (i.e. anti-virus) protection software with SharePoint Server, please excluded certain folders from antivirus scanning.
2.You could try to clear browser cache then restart it.
3.Try to use a different browser or your browser's InPrivate mode to see if the same error occurs.
4.Please try to restart IIS of the web application to see if the same error occurs.
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