List of problems that are slower than expected

[Wikunia]

I want to use this issue to track problems that are slower than expected.
These problems will need some testing with profiling, tree visualization and other tools.
There might be a variety of reasons like:

• bad pruning
• slow because of memory consumption
• not the best search strategy

Current list:

• Adding a variable slows down the search: Adding a variable slows down the search #200
• Steiner.jl:
  old formulation: n=7 in 0.04s, n=9 in 4.1s
  new formulation: n=7 in 0.07s, n=9 timeout (>6s) (with &&)

Please add a comment with a link to the model (or the model itself) for which the solver than expected.