That `generating syntax summary` is from Sublime Text. You can try disabling it by going to the menu `Preferences -> Settings` and setting `"index_files": false`
Alternatively, you can try to limit the number for CPU's Sublime Text will use to index files by setting `"index_workers": 1` instead of completely disabling the file indexing:
Code:
// File indexing parses all files in the side bar, and builds an index of
// their symbols. This is required for Goto Definition to work.
"index_files": true,
// Set the number threads to use for indexing. A value of 0 will make
// Sublime Text guess based on the number of cores. Use the index_files
// setting to disable all workers.
"index_workers": 0,