When I process files using the latest standalone  ConTeXt  ver: 2019.04.29 08:52 MKIV beta  fmt:  LuaTeX, Version 1.10.0 (TeX Live 2019)), I now get the following error message:

lua error       > lua error on line 8 in file env_Brill-01.tex:


...eXt/tex/texmf-context/tex/context/base/mkiv/font-oup.lua:1317: bad argument #1 to 'concat' (table expected, got number)


The error log is as follows:

return {
 ["filename"]="env_Brill-01.tex",
 ["lastcontext"]="\
\\font_helpers_low_level_define ...nsize }{\\m_font_designsize }\\scaledfontmode \
                                                  \\relax \\ifcase \\scaledfont...\
\\font_fallbacks_clone_unique ...w_level_define {#1}\\v_font_identifier_basic \
                                                  \\csname \\v_font_identifier...\
l.8 }\
    \
\\font_fallbacks_prepare #1->\\clf_fontcollectionprepare {#1}\
                                      \
\\font_fallbacks_prepare_indeed ... \\lastrawfontcall \\font_fallbacks_prepare #1\
                                                  \\endgroup \
<inserted text> ...nt_fallbacks_prepare_indeed \\m_font_fallbacks \
                                                  \\fi \\fi \
...\
l.215 \\setupbodyfont[mainface, 10pt]\
                                   ",
 ["lastluaerror"]="...eXt/tex/texmf-context/tex/context/base/mkiv/font-oup.lua:1317: bad argument #1 to 'concat' (table expected, got number)",
 ["lasttexerror"]="?",
 ["linenumber"]=8,
 ["luaerrorline"]="1317",
 ["offset"]=10,
}

This files process as they should with earlier versions. I will try to produce an mwe if needed but hope that it is not.

Alan