Occasionally "Add" throws a non-sensical "Not a properly named namespace"

[aplteam]

Describe the bug

...
Link @ 08:27: Deleted #.MarkAPL.MarkAPL.API (C:/T/Projects/APLTree/MarkAPL/APLSource/MarkAPL/API)
⎕SE.Link.Add: Not a properly named namespace:  #.MarkAPL.MarkAPL.API 
CreateAPI[132] {}⎕SE.Link.Add fullName
      #.MarkAPL.MarkAPL.⎕nc'API'
0

The problem is that when I trace through the code after this error was thrown then Add returns a message that reads "Not found: #.MarkAPL.MarkAPL.API.CompressCSS" rather than throwing the error again.

When I restart from scratch everything works fine...

      ]tooLS.Version
 Dyalog  18.2.47418 32-bit Unicode, BuildID c8e80564            
 OS      Windows 10 or Windows Server 2016 (10.0.19045) 32-bit  
 Link    3.0.19                                                 
 SALT    2.9                                                    
 UCMD    2.51                                                   
 .NET    .NET Framework 4.8.9181.0                              
 Tatin   0.103.1-beta-3                                         
 Cider   0.37.5                                                 
 WS      18.2                                                   

I've seen this three times now over the course of the last ~4 months.
It happened in 18.2 and 19.0