- Disable code folding at Configuration - Editor Display - Code Folding and test if this makes already a difference.
- Next uncheck Enable syntax coloring at Configuration - Editor Display - Syntax Highlighting and test if this makes now a difference.
- If code folding and syntax highlighting makes no difference, enable both options again, and select for both files No Highlighting at View - View as (Highlighting File Type). That turns off code folding, syntax highlighting and the scan for function strings for the function list view. Test if toggling the active file is fast now.
In general it is advisable for C/C++ to look on the regular expression strings used to find functions and since UE v16.00 also the function parameters and local variables and adapt and remove what not needed for your files. For example if you are working only with C files, you can remove the regular expressions used for C++. Further the expressions in standard wordfile c_cplusplus.uew are defined to match as many different C/C++ coding styles as possible. Adapting them to what you really need for your coding style and eliminate those not really needed for your files improves performance a lot. A simple test to find out what is needed and what could be removed is to use the regular expressions as you can see in the wordfile in a Find in Files searching in all your *.c files. If such an UltraEdit regular expression finds no string in any of your *.c files or just non function strings found, you can remove that regular expression from your wordfile.