There is an known issue for Apollo 2018, user's custom EPSG code doesn't work with crawled vector data, WMS rendering will not work. The same custom EPSG will work with crawled raster images.
The following workflow will provide workaround for this issue.
C:\Program Files\Hexagon\ERDAS APOLLO\lib\etc\projections\epsg.plb
Recycle the DecodingService app pool by executing "C:\Program Files\Hexagon\ERDAS APOLLO\tools\RegisterEPSGCodes\bin\RegisterEPSGCodes.exe" and then select the button to recycle IIS App Pools.
The module, Intergraph.Apollo.DecodingService.Repository.CGPExtensions, records debug messages and should display something similar to the following:
epsgCode=EPSG:99999 (your custom code)
Retrieving crs id for moniker: 1,1,0,13/1024,1/2048,32767/2050,6326/3072,32767/3074,32767/3075,1/3076,9001/3080,29.000000000000007/3081,0.0/3082,0.0/3083,2600000.0/3092,1.0/4096,5773 and crsIdType:EPSG.
Copy the moniker string, "1,1,0,13/1024,1/2048,32767/2050,6326/3072,32767/3074,32767/3075,1/3076,9001/3080,29.000000000000007/3081,0.0/3082,0.0/3083,2600000.0/3092,1.0/4096,5773" and save it.
<EPSGCode> <number>20533</number> <moniker>1,1,0,13/1024,1/2048,32767/2050,6326/3072,32767/3074,32767/3075,1/3076,9001/3080,29.000000000000007/3081,0.0/3082,0.0/3083,2600000.0/3092,1.0/4096,5773</moniker> </EPSGCode>