the format ./IOTABLE="CP1252" applies only using the OPEN command

$ZCONVERT and %Stream.FileCharacter  just use "CP1252" just by the name

In namespace %SYS you have a utility NLS that shows your installed conversion table and its short names.

%SYS>d ^NLS
2) Select defaults
2) I/O tables
Items marked with (*) represent the locale's original default
 I/O table              Current default
---------------------  --------------------
1) Process             RAW (*)
2) Cache Terminal      UTF8 (*)
3) Other terminal      UTF8 (*)
4) File                RAW (*)
5) Magtape             RAW (*)
6) TCP/IP              RAW (*)
7) System call         RAW (*)
8) Printer             RAW (*)
 
I/O table: 4
 
 1) RAW (*)                              2) UTF8
 3) UnicodeLittle                        4) UnicodeBig
 5) CP1250                               6) CP1251
 7) CP1252                               8) CP1253
 9) CP1255                              10) CP437
11) CP850                               12) CP852
13) CP866                               14) CP874
15) EBCDIC                              16) Latin2
17) Latin9                              18) LatinC
19) LatinG                              20) LatinH
21) LatinT

So you see the shortnames but no Latin1  but CP1252 which is almost identical.
the related problem is described here:
 https://www.i18nqa.com/debug/table-iso8859-1-vs-windows-1252.html

"ISO-8859-1 (also called Latin-1) is identical to Windows-1252 (also called CP1252) except for the code points 128-159 (0x80-0x9F). ISO-8859-1 assigns several control codes in this range. Windows-1252 has several characters, punctuation, arithmetic and business symbols assigned to these code points."

and Encoding Problem: ISO-8859-1 vs Windows-1252
So you should check what your customer really does (some hide the fact they use Windows)

The appropriate table can be used in

• $ZCONVERT(),
• ##class(%Stream.FileCharacter ) property TranslateTable
• OPEN command parameter /IOTABLE=

SUPER ! 

Robert

Sorry!  That doesn't indicate any reason. $zf(-1) is just a spawn.

using LOG^%ETN gives a full stack trace. without breaking the process
you just have to place it into your code at the critical points.
https://docs.intersystems.com/iris20201/csp/docbook/Doc.View.cls?KEY=GCOS_errors#GCOS_errors_log_etn

Instead of the double $ZF()  I'd suggest using the query in Library class %File.

 
set rs=##class(%ResultSet).%New("%File:FileSet")
do rs.Execute(SDIR,"*",1)
while rs.Next() { write !,rs.GetData(1) }

Let's analyze this:    [leaving aside that $Zf(-1 .. is Deprecated)

1. You run the same sequence in 2 Caché/IRIS  processes in parallel.
2. There is no synchronization between them
3. Both run in the same namespace ==> therefore the same default directory where SDIR_"DIRLIST.TXT" is located ???? " .. but from a different folder... "    is SDIR different ????? if not :
4. Both processes spawn 2 times a sub-process for each $ZF(-1)
5. let's name the sub processes fg1, fg2 and bg1,bg2
6. The sub_process from foreground is not synchronized to the sub-process of background and your construct has no control on the sequence they are running.
7. If the run sequence  fg, fg1,fg2,bg,bg1,bg2  there should be no problem. But that's rater unlikely
8. it looks like fg,bg,fg1,fg2,bg1 (partially deleting results of fg2), bg2  

To verify what's really happening run fg,fg1,fg1,bg (JOB ), bg1,bg2   
So they both can't influence each other.

You may use this at init time  
https://openexchange.intersystems.com/package/helper-for-objectscript-language-extensions   
to add your ZPM command and function. It does a unique insert of the label

@Vic Sun. your reaction is - to formulate it politely - a disappointment.
But no surprise to me.

I understood that 14 licenses + Grace Period are your biggest pains.
In past, I  decreased the risk by moving ALL (suspicious) connections to a dedicated  User
observing his maxConnection limit using %CSP.Session.Login() especially this explanation:

This can't avoid a DDoS attack but it limits the initial impact and allows you to
protect some emergency licenses.

[As I know the inventor of Grace Period since it was rolled out with a lot of pain for customers
I'm not willing to discuss this "feature" in public again]

as you are in SMP anyhow just try to do an insert manually.
Just 1 row.
you seem to require something else <UNDEFINED>
in addition, if your record exists already You may need an 
INSERT OR UPDATE   (if this is possible in postgreSQL)

It could be OK, but I wonder that you insert just 1 value
Eventually, there is something required that is missing?
Check the definition of the generated Caché class,
 

Seems just a typo in INSERT statement.
Target Columns must be in parenthesis.

INSERT INTO HSIPIData.datos_usarios2 (addresses)
       SELECT Addresses FROM HSPI_Data.patient