Since these "trouble" tests (actually step text in tests) come from an import from Excel, we suspect this very COMMON problem is related to "illegal"/bad characters in the text string(s) that came across into the steps table.
To remedy this, you will need to go into the test(s), then into each "trouble" step select ALL text in the cell/box for a given step/column and CUT (removes ALL text) the text out of the box, then PASTE into Notepad to try to "clean" it up, then copy that "clean" text and PASTE it back into the step where it came from (the QC test/step/cell text box should be empty and contain NO characters from previous save). Then, you can arrange/format it the way you want from within QC with it's text tools.
If Notepad does not scrub out the "offending" characters, you may need to use a more powerful editor like Notepad++ which can highlight the characters from the extended character set so you can remove them.
The problem is that when bringing in text (copy/paste or via import tool) from Excel or Word, we sometimes see excessive markup/formatting to cause much trouble in QC, so it is best to scrub or clean up the text to get rid of these bad characters (many non-printing/invisible) as they can cause unexpected formatting or even crash QC grids. HP/HPE now MicroFocus has tried for many years to delicately strip out the bad characters automatically without destroying the original text, but has to make judgement calls on what to take out and what to leave, so sometimes bad characters still get in -- especially with cross-language teams.
So, the rule of thumb is to strip everything of "heavy" formatting (bullets, colors, etc.) BEFORE trying to import or use copy/paste into QC.
Hope this helps,