There is a setting for maximum number of matches for highlighting symbol under cursor, it is not listed under Tools > Options, that needs to be fixed. But, you can change it on the SlickEdit command-line, set-var def_highlight_symbols_max_matches. The default is set to 100 matches. There is also a timeout for symbol highlight searching, which is in Tools > Options > Editing > Context Tagging > Maximums > Maximum response time (ms) for highlighting matching symbols, it defaults to 1000 millisecs.
