Not saving and recalling a custom CRS for a project

[Derrick-Wells]

I use a custom CRS and have saved it as part of the projects properties (menu Project / Properties / CRS tab. The custom CRS is USER:100000 with parameters +proj=lcc +lat_1=-33.3333333333 +lat_2=-26.6666666667 +lat_0=-35 +lon_0=23 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs

When checking on the project properties it indicates both the project_crs as USER:100000 and project_crs_definition as above.

Also note that the default CRS is also set as USER:100000 (set in Settings / Options / CRS and set Use a Default CRS.

On opening QGIS it does indicate the default CRS as USER:100000 however when opening a project where the CRS is set to USER:100000, the CRS changes to Unknown and in the projects variables the project_crs is blank but project_crs_definition still contains the correct values.
Error of Default CRS set to USER.docx

[Derrick-Wells]

Using QGis vs 3.12.3 on Windows - this error also exists in the current LTR.

[nyalldawson]

The correct solution here is to ensure your custom CRS is set to use a "WKT" string, not a "PROJ" string. It's easy to change -- from the Custom Projections dialog, select your CRS, and then change Format to "WKT (recommended)".