I think I might have found the reproducibility problem:

src/Makefile has a line

> ./src/Makefile:COMPTIME                := $(shell date +%s)
and

./src/Makefile:    $(CC)    $(CFLAGS_NATIVE) $^ -o $@ $(HASHCAT_LIBRARY) 
$(LFLAGS_NATIVE) -DCOMPTIME=$(COMPTIME) -DVERSION_TAG=\"$(VERSION_TAG)\" 
-DINSTALL_FOLDER=\"$(INSTALL_FOLDER)\" 
-DSHARED_FOLDER=\"$(SHARED_FOLDER)\" 
-DDOCUMENT_FOLDER=\"$(DOCUMENT_FOLDER)\"

comptime seems to be only ever set, never actually used, so it should be 
safe to replace it with 0. I'll try a patch.