error at ./Distribution/Client/Dependency.hs:823:33

Hello.

Debian Haskell Group maintains number of haskell applications and
libraries, some of which are not on stackage. Before starting
packaging, list of packages and their version, called "plan" is
established.

To check, whether all these packages can be correctly installed
together, script is used, that generates very long invocation of
cabal-install(1), like following:

cabal [...] install --dry-run --force-reinstall --max-backjumps -1 \
--constraint 'cabal-debian -local-debian'
--constraint 'chell color-output' [...]

Since Debian patches some of haskell packages and have some additional
packages, not present in Hackage index, index file 01-index.tar is
patched accordingly before feeding it to cabal(1).

Under some circumstances (problem is reproducible) cabal(1) exits with
error, without expaining what is wrong:

CallStack (from HasCallStack):
error, called at ./Distribution/Client/Dependency.hs:823:33 in
main:Distribution.Client.Dependency

Several pages above there is following text:

internal error: could not construct a valid install plan.
The proposed (invalid) plan contained the following problems:
Package lens-4.16.1 has an invalid configuration, in particular:
missing an assignment for the flag: test-templates

You can see whole output of cabal(1) on Gitlab CI page[1]. Any
ideas, what can be wrong and how to fix it?

[1] https://salsa.debian.org/haskell-team/package-plan/-/jobs/176658