In case anyone else is having a similar issue, over the last couple days I've had three scan stations at two different clients be unable to save the Laserfiche Scan Source setting. Every time LF Scanning is open it asks for the scan source.
In all cases CCleaner had recently been run on the station. All scan stations were running LF 8.3 and either Windows 7 or 10.
A repair on the LF Client resolved the issue.
Apparently some recent update to CCleaner is causing an issue (with 8.3.x scanning at least).