I've discontinued roxterm because the amount of work needed to fix
outstanding bugs and continue to maintain it was more than it was worth.
gnome-terminal is pretty good these days, and there are other terminals.
This bug looks like it's caused by an ABI change in VTE, which you would
need roxterm version 3 for, but there was also another nasty
incompatibility with GTK 3.20, hence its removal from Debian.
If you really badly want to keep using roxterm and don't mind missing
some features you could try roxterm-gtk2.