I'm looking for some help with problem with the linker being unable to locate the _write method in a release build only. 

I'm working on an older project (last built in 2019) that I can't seem to get to build in the Release configuration. No problems with the Debug configuration. The error is:

ld.exe: .o): in function _write_r

Error linking for board Teensy 3.2 / 3.1 (teensy31)
(.text._write_r+0x14)*: undefined reference to _write
Build failed for project 'Eyedrivomatic.Firmware.Delta'

I have the "Arduino 2" IDE selected with the default locations. I've tried re-installing the Teensy board files. Am I missing a library location? If so, where would I specify it?

Note: the build output shows that I am using a trial version. However, I was using a licensed version the last time I built this project. I fully intend to renew my license assuming I can get this to build again.