Incorrect Results from IfFileExists with updates to TeXLive2020

Following an update to my packages with TeXLive2020 I am seeing different behaviour than in TeXLive2019. The following test is run in the directory Testing/ which besides the MWE in the file entitiled foo-x-bar.tex & foo-x-bar.pdf contains only the MacOS .DS_Store (but no other files).

With TeXLive 2020 (with latest updates applied), it outputs:

where as with TeXLive2019 I obtain the correct results:

Notes:

• The other change I had to make with an update to the packages in TeXLive2020 is to handle the fact that themainfile is sometimes reported as ./foo-x-bar.tex whereas with TeXLive2019 (and earlier TeXLive2020 before the package updates) it was foo-x-bar.tex (ie, without the leading ./). The use of IfBeginWith resolves that issue, but including it here so that this code works either way.

• Surprisngly, in my actual use case I am seeing the opposite results. The file exists but is being reported with an updated TeXLive202 as it does not exist!! Will continue to attempt to produce an MWE with that result if the solution to this does not resolve my issue.

listfiles 2020

 article.cls    2020/04/10 v1.4m Standard LaTeX document class
  size10.clo    2020/04/10 v1.4m Standard LaTeX file (size option)
  xparse.sty    2020-10-27 L3 Experimental document command parser
   expl3.sty    2020-12-07 L3 programming layer (loader) 
l3backend-pdftex.def    2020-09-24 L3 backend support: PDF output (pdfTeX)
 xstring.sty    2019/02/06 v1.83 String manipulations (CT)
currfile.sty    2020/09/29 v0.7d Provides the file path elements of the current
 input file
kvoptions.sty    2020-10-07 v3.14 Key value format for package options (HO)
  keyval.sty    2014/10/28 v1.15 key=value parser (DPC)
 ltxcmds.sty    2020-05-10 v1.25 LaTeX kernel commands for general use (HO)
kvsetkeys.sty    2019/12/15 v1.18 Key value parser (HO)
filehook.sty    2020/09/29 v0.8a Hooks for input files
filehook-2020.sty    2020/09/29 v0.8a Hooks for input files
currfile-abspath.sty    2020/09/29 v0.7d Provides absolute file paths, the pare
nt working directory and the main file name

listfiles 2019

 article.cls    2019/10/25 v1.4k Standard LaTeX document class
  size10.clo    2019/10/25 v1.4k Standard LaTeX file (size option)
  xparse.sty    2019-10-11 L3 Experimental document command parser
   expl3.sty    2019-11-07 L3 programming layer (loader) 
expl3-code.tex    2019-11-07 L3 programming layer 
l3deprecation.def    2019-04-06 v L3 Deprecated functions
l3backend-pdfmode.def    2019-04-06 L3 backend support: PDF mode
 xstring.sty    2019/02/06 v1.83 String manipulations (CT)
currfile.sty    2015/04/23 v0.7c Provides the file path elements of the current
 input file
kvoptions.sty    2016/05/16 v3.12 Key value format for package options (HO)
  keyval.sty    2014/10/28 v1.15 key=value parser (DPC)
 ltxcmds.sty    2016/05/16 v1.23 LaTeX kernel commands for general use (HO)
kvsetkeys.sty    2016/05/16 v1.17 Key value parser (HO)
infwarerr.sty    2016/05/16 v1.4 Providing info/warning/error messages (HO)
etexcmds.sty    2016/05/16 v1.6 Avoid name clashes with e-TeX commands (HO)
ifluatex.sty    2019/10/25 v1.5 ifluatex legacy package. Use iftex instead.
   iftex.sty    2019/11/07 v1.0c TeX engine tests
filehook.sty    2019/10/03 v0.6 Hooks for input files
currfile-abspath.sty    2015/04/23 v0.7c Provides absolute file paths, the pare
nt working directory and the main file name

Code:

To match the results, create a directory Testing/ and save the following MWE as Testing/foo-x-bar.tex.

documentclass{article}
usepackage{xparse}
usepackage{xstring}
usepackage[realmainfile]{currfile}% 


AtBeginDocument{%
    getmainfile
    IfBeginWith{themainfile}{./}{%
        StrBetween[1,2]{themainfile}{./}{.}[FileNameNoExtension]%
        typeout{Used Used stringStrBetween}%
    }{%
        StrBefore{themainfile}{.}[FileNameNoExtension]%
        typeout{Used stringStrBefore}%
    }%
}%

NewDocumentCommand{GetTexFileNameWithPath}{}{%
    ../Testing/FileNameNoExtension.texxx%
}%

listfiles
begin{document}
The file name extracted from verb|themainfile| is FileNameNoExtension.

defFileNameWithPath{GetTexFileNameWithPath}%
IfFileExists{FileNameWithPath}{%
    File ``FileNameWithPath'' exist.%
}{%
    File ``FileNameWithPath'' does emph{NOT} exist.%
}%
end{document}

documentclass{article}
protecteddefFileNameWithPath{../Testing/foo-x-bar.texxx}%
begin{document}
File ``FileNameWithPath''
IfFileExists{FileNameWithPath}{}{emph{NOT} }exist.
end{document}