This should be a simple case of one line adjustment behaves the same for everyone BUT
The idea of command line adjustments is they should normally (but not always) work well where broken parts are
"surrounded by double quotes"
Unfortunately cut and paste in a forum can itself be a problem, and the older images above were deleted by the discourse system !
However there are some cases where there is interference by mismatch or other symbols such as here seen by your text near the \ - but your image says more.
The intention here is that when Zotero calls SumatraPDF with a Page reference the command line is slightly adapted
Acrobat /A page=123 "and filename" becomes
SumatraPDF -page 123 "and filename"
That is done via the acro2suma.cmd by ignoring %1 (the /A part) and changing %2 (the page part) by adding a - in front of it without a space
What is happening in this case is that when double clicking the command is started but without any valid page request and file name it would therefore in SumatraPDF appear to be asking to open a file simply named “-” (actually if there is a file called “-” it will open it and wait for the next in the line)
The solution is a more complex IF page requested DO this, ELSE DO that.
so the CMD file just needs to see if %2 is “page” otherwise we could assume that %1 etc. is NOT /A but perhaps the filename
To Keep It Stupidly Simple (KISS) we just need to do something like an inelegant
@if /i [%1]==[/A] start "" "C:/Program Files (x86)/SumatraPDF/SumatraPDF.exe" -reuse-instance -%2 %3 %4
@if /i not [%1]==[/A] start "" "C:/Program Files (x86)/SumatraPDF/SumatraPDF.exe" -reuse-instance %1 %2 %3 %4