Looking at the line: https://git.sr.ht/~sthagen/liitos/tree/default/item/liitos/render.py#L181
it is clear that many lines may fulfill this condition and then fail in a naive split call:
for slot, line in enumerate(lines):
if '.svg' in line and line.count('.') >= 2:
caption, src, alt, rest = con.parse_markdown_image(line)
stem, app_indicator, format_suffix = src.rsplit('.', 2)
Fixed per commit 98d01c6 will be available with next release.