COBYLA seems to hang on the following code:

https://gist.github.com/bluescarni/bdb1981c80966ebae5d92551b605347d

Compilation command line, on 64bit linux GCC 6.3 and NLopt 2.4.2:

g++ -std=c++11 -O2 -DNDEBUG file.cpp -lnlopt -march=native

If the dimension of the problem is changed, from 150, to 149 or 151, the optimisation does not hang. If the dimension is 150, the optimisation seems to hang after ~170 objfun/constraint evaluations (strangely enough, the exact number is 171 on my Gentoo linux installation, and 175 on my Arch linux installation).

The optimisation problem is No. 5.1. from Luksan, L., and Jan Vlcek. “Sparse and partially separable test problems for unconstrained and equality constrained optimization”. It has only equality constraints.

http://folk.uib.no/ssu029/Pdf_file/Luksan99.ps