Dear Hans, 

Here is a small example which shows a strange spacing in the aligned display math mode.
The same code is OK in both inline mode and just display mode, but it is not good in aligned mode.

I hope that it helps your fix .

Thank you.

Best regards,

Dalyoung

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running luametatex version 2.03.3,   ConTeXt ver: 2019.12.12, format: 2019.12.14
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\starttext
\startitemize
\head inline formula:

$1001 \times 23 \equiv 1 \quad \pmod {3837}$

\head display mode

\startformula
1001 \times 23 \equiv 1 \quad \pmod {3837}
\stopformula

\head aligned display mode

\startformula\startalign[m=2]
\NC 2^7 \equiv \qquad \NC \pmod {341}, \NC 14^7 \equiv \qquad \NC \pmod {341}, \NR
\NC 11^7 \equiv \qquad \NC \pmod {341}, \NC 3^7 \equiv \qquad \NC \pmod {341}, \NR
\stopalign\stopformula

\startformula\startalign[n=3]
\NC 1001 \times 23 \NC \equiv 1 \quad \NC\pmod {3837} \NR
\NC \qquad \times 23 \NC \equiv \qquad \NC\pmod {3837} \NR
\stopalign\stopformula

\stopitemize
\stoptext