Unexpected behavior: `ancient` keyword may trigger Snakemake scheduler issues

When running metaG samples through imp3 [commit ecead78b], I noticed the following message/warning in the SLURM log file:

Failed to solve scheduling problem with ILP solver in time (10s). Falling back to greedy solver.

While it doesn't cause any issue per se, I noticed that the jobs are taking longer to complete. I can't necessarily confirm this yet, and the sample is still running, but I've attached the SLURM log.
A little digging revealed an issue with snakemake when the keyword ancient is used. See here: https://github.com/snakemake/snakemake/issues/946
I noticed that imp3 uses this keyword in the function.definitions rule

Something to keep an eye on for the future ;)