There's a 256 character limit on entries in the table of contents. The problem is that the limit is calculated before Logos markup is handled, not afterwards. So if your markup is lengthy , then your TOC entries will be truncated.
In my case I had an entry which said:
[[@Page:3215]][[@Headword:Church Father]][[@Headword:Early Church Fathers]][[@Headword:Early Church Father]][[@Headword:Greek Fathers]][[@Headword:Holy Fathers]][[@Headword:Fathers of the Church]][[@Headword:Latin Fathers]][[@Headword:Church Fathers]]Church Fathers
Which was truncated to 'Churc'.
It's an even bigger problem when the 256th character is in the middle of a bit of Logos' markup. So another example:
[[@Page:3254]][[@Headword:Church of God (7th day) - Salem Conference]][[@Headword:General Conference of the Church of God (Seventh-Day)]][[@Headword:Church of God (7th day)]][[@Headword:Church of God (Seventh Day)]][[@Headword:Church of God (7th day) – Salem Conference]][[@Headword:Church of God (Seventh-Day)]]Church of God (Seventh-Day)
This became a TOC entry of '[[@Headword:Church of God (7th day) – Sal'.
Although I'm giving headwords as an example, the problem would also be likely to occur if you had URL links in your headings.
The solution, presumably, is to parse the markup, then truncate, rather than the other way around.