Sudden Loss of Pwr: K Bike: Try "contact enhancer" on big computer connector
I've solved this problem with NAPA "contact enhancer" CE-1, $70, aka Stabilant 22. The eye dropper bottle comes with "Q tips" to touch the posts and or the pinching finger tips of the computer connectors and others. The fluid will make a hissing sound as it cleans off the slow buildup of 15+ years of corrosion that also servers as a growing insulator. This stuff makes fuel injectors behave better when you touch their connector parts. It has helped numerous older fuel injected cars and bikes I've owned. I carry the bottle and Q tips to rallies in hopes of helping people like you. I've helped a few.
Sometimes just opening and closing a connector causes enough "rubbing" to clean off corrosion. Connectors are best designed if they wipe as plugged in and out. New parts installed also perform the wiping of the other connector, so the new part appears to have solved the problem when the old part with cleaner connectors would have been fine too. I also think many K bikes go for sale because the owner has trouble like yours and can't "trust" them anymore and then try some expensive troubleshooting . . . when clean connections could really make a big difference.
My 85 K100RS with 146,000 miles hasn't needed many parts, mostly just connector cleaning when trouble pops up. I have done several of the K bike tech page switch cleanings etc. as well.
Waiting a week or so for the bottle and spending $70 years ago felt bad, but since then using it has felt so good every time, many old Volvos, an old BMW 525i, several old K bikes, some old Chevy Suburbans. The fuel injection, computer and signal connectors are real low voltages so connector resistance can wreak havoc when beyond a decade old.