The problem with too many continuation lines causing a segfault was happening on my MacBook (MacOS Sierra) with an old version of gfortran:
gfortran --version
GNU Fortran (Homebrew GCC 7.2.0) 7.2.0
So I moved the code to another platform and tried it with 3 different compilers: Cray, Intel, and gfortran 8.3.0 . There was no problem in those 3 cases.
So the problem appears to be due to using an old version of gfortran on my Mac.