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

**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