After Windows 2008 R2 patches were applied, SQL*Plus connections failed with ORA-12631. I couldn't find a match on the Oracle support site, so I had to do more digging. By enabling SQL Tracing on the server side, I tracked down OS error messages that matched in KB4480970 and KB4480960. Microsoft has a fix, KB4487345, which worked for us.
Large pages are important for performance of instances with large SGAs, and the mixed mode of allocation in Windows is a good idea. Unfortunately, it has been poorly implemented, leaving Oracle DBAs without an ideal configuration option.
RMAN duplicate from backup location fails with RMAN-05579 on Windows. Turns out, RMAN on Windows requires UNC paths rather than mapped drive letters for network shares.
EM Express calls WRI$_REPT_SQLPI, generating a SQL statement with a cartesian join involving DBA_ADVISOR_OBJECTS, which can use 100% CPU for hours.
SQL*Plus 12.2 ignores %SQLPATH%\LOGIN.SQL
Enabling OS authentication for Oracle databases running on Windows prevents password authenticated connections from other domains without trust relationships. Eg, RMAN running in the pre-production domain wouldn't be able to use a database account password to connect to an RMAN catalogue database in the production domain.
The Oracle database may be prevented from removing datafiles when a tablespace is dropped (including contents and datafiles) on Windows, even with Oracle 12.1.