With modding tr levels with these tools comes some risks as they're all very caringly fan made! But a long time ago now with little updates. Blood appearing as bubbles and other Sprite errors are a sign that perhaps you've edited a little too much in the level or, saved it a few times already via trviewer etc...there may be a more thorough explanation but that's how I've always interpreted it as I could never fix it
unless you start again! I keep a backup copy of my TR games Data folders so instead of numerously modding a specific file over and over, starting on a fresh unedited one each time reduces the likelihood of something breaking eek!
There is an option in trviewer from memory that allows you to keep unused textures when saving - trial and error with yes and no with this option if you come across sprite issues and other texture stuff.