The following:
\setupdirections[bidi=global]
\definefallbackfamily[mainface][serif][SBL Hebrew][range={0591-05F4,FB1D-FB4F}]
\definefontfamily[mainface][serif][TeX Gyre Termes]
\setupbodyfont[mainface, 10pt]
\starttext
xxxx yyyy zzzz \setupalign[rtl]{
ﬡﬡﬡﬡﬡﬡﬢﬢﬢﬢﬢ
}
\setupalign[ltr]aaaa bbbb
\stoptext
 sets as it should with ConTeXt  ver: 2018.09.13,  LuaTeX, Version 1.09.0 (and several betas later).

But with ConTeXt  ver: 2019.05.12, LuaTeX, Version 1.10.1
it complains with:
lua error       > lua error on line 8 in file ...test-03.tex:

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

 1     \setupdirections[bidi=global]
 2     
 3     \definefallbackfamily[mainface][serif][SBL Hebrew][range={0591-05F4,FB1D-FB4F}]
 4     
 5     \definefontfamily[mainface][serif][TeX Gyre Termes]
 6    
 7     \setupbodyfont[mainface, 10pt]
 8 >>  
 9     \starttext
10     xxxx yyyy zzzz \setupalign[rtl]{
11     ﬡﬡﬡﬡﬡﬡﬢﬢﬢﬢﬢ
12     }
13     \setupalign[ltr]aaaa bbbb
14     
15     \stoptext
16     

mtx-context     | fatal error: return code: 256

Has something changed in how such l2r fonts should be invoked?

Alan