Missed keyboard inputs in Slack and Bear but not in other apps

My late-2013 13" MacBook Pro recently started missing some keyboard inputs in _some_ applications, particularly [Slack](https://slack.com) and [Bear](http://www.bear-writer.com) , and especially (but not only) when I'm in a Google Hangout video call. Hangout typically hogs the CPU when running in Safari and typing on Slack results in missing characters (not just delayed!). Interestingly, typing in Sublime Text always works fine. 1. What makes Slack and Bear more likely to miss inputs when the CPU is overloaded? Slack is running on the notably slow framework Electron but I don't believe Bear is. 2. Is anybody else noticing this behavior? 3. My Mac is up to date and uses an SSD and 16GB of RAM, but it's also 5 years old. Would a brand new MacBook 12" run Hangout and Slack more efficiently?