I updated the client (VB Coastal) to version 16.6, which caused an 'Ambiguous Reference' error in a custom check-in block. The client uses a custom check-in block for batch printing labels:
https://rock.vbcoastal.com/admin/cms/file-manager/edit?RelativeFilePath=%7e%2fPlugins%2forg_newpointe%2fCheckinBatchCut%2fCustomCheckinSuccess.ascx.cs
The same error was fixed in another plugin called 'Attended Checkin', which was created by New Spring and is maintained by KFS. The supported plugin lives here: https://www.rockrms.com/rockshop/plugin/32
The error originates from the New Pointe Check-in Batch Cut plugin, which lives in github: https://github.com/NewPointe/rock-plugin-checkinbatchcut/tree/master. It is not available from the RockShop and does not appear to be supported. I copied the fix over from the supported plugin to the un-supported plugin: