My savegame starts right before an inconvenient fight with a Hell Knight. I noticed that most of the time the first hit from the Hell Knight appears to deal no damage (Ouch sound, red flash, but HP displays 61). Second and further hits work as expected.
I attached the savegame. Take the rad suit and jump into the canal. You need Alien Vendetta wad: <!-- m --><a class="postlink" href="http://www.doomworld.com/idgames/index.php?id=11790">http://www.doomworld.com/idgames/index.php?id=11790</a><!-- m -->