After applying 9.2SP2 CU18, 9.1SP3 CU43 or 9.0SP3 CU29, Ektron date selectors and other xslts will fail to fully load. You may see this in the CMS or on the frontend of the site. Here you can see this in the schedule tab. 

This issue is fixed in a site cumulative update.

9.2 SP2 CU19, 9.1 SP3 CU44, 9.0 SP3 CU30

• EKTR-466: Increase permissiveness of loading known XSLT files

Apply the latest CU to resolve this issue. 

Downloads and Install Instructions

As a workaround, add the following file to the XSLT whitelist. Any other custom XSLTs should be whitelisted as well.

C:\inetpub\stage\WorkArea\calendarAdmin\xslt\calendaradmin_dtselectordatetime.xsl

How to add acceptable XSLT files to the system

Add the following line to the whitelist file.

<xslt>calendarAdmin\xslt\calendaradmin_dtselectordatetime.xsl</xslt>