Ok ... well at the time that was posted no delays were expected however the IRS shut down many departments when they sent the workforce home 2 months ago and they are just getting back to work. The 60 day notice you got told you the return was being reviewed. Reviews are done by humans which were is short supply. You will probably be getting a second 60 day letter soon.
From the IRS :
The return data is then transmitted to the Martinsburg Computing Center, where it is subjected to math error and validity checks before attempting to post to the IRS Master File. If no errors or inconsistencies are found and all requirements are met, refunds or balance due notices are issued to the taxpayer.
Return data with errors or inconsistencies is transmitted back to the processing centers where tax examiners make corrections using an Error Resolution System. The corrected return data is transmitted back to the computing center and attempts to post to the IRS master file.
https://www.irsvideos.gov/Professional/IRSWorkProcesses/SubmissionProcessingPipeline
