keyboard backspace

Does yours qualify for Keyboard Service Program for MacBook, MacBook Air, and MacBook Pro...

https://support.apple.com/keyboard-service-program-for-mac-notebooks

Eligible Models

To identify your computer's model and to see if it is eligible for this program, choose Apple () menu > About This Mac. Eligible models are listed below.

▪ MacBook (Retina, 12-­inch, Early 2015)

▪ MacBook (Retina, 12­-inch, Early 2016)

▪ MacBook (Retina, 12-­inch, 2017)

▪ MacBook Air (Retina, 13-inch, 2018)

▪ MacBook Pro (13­-inch, 2016, Two Thunderbolt 3 Ports)

▪ MacBook Pro (13-­inch, 2017, Two Thunderbolt 3 Ports)

▪ MacBook Pro (13-­inch, 2016, Four Thunderbolt 3 Ports)

▪ MacBook Pro (13-­inch, 2017, Four Thunderbolt 3 Ports)

▪ MacBook Pro (15-­inch, 2016)

▪ MacBook Pro (15-­inch, 2017)

▪ MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)

▪ MacBook Pro (15-­inch, 2018)

▪ MacBook Pro (13-inch, 2019, Four Thunderbolt 3 Ports)

▪ MacBook Pro (15-­inch, 2019)

Note: No other Mac notebook models are part of this program.

https://www.apple.com/support/keyboard-service-program-for-mac-notebooks/

Interesting situation, the two things that come to my mind are either that particular key on your keyboard is physically starting to fail in some way, or the "delay until repeat"/"key repeat" settings were changed somehow in System Preferences.

If you haven't already tried this, go to System Preferences, select "Keyboard" and on the first tab check the position of the sliders to make sure they're in a 'normal' position, then try backspacing text again:

I know that you're only having this double/triple press problem with only that particular key, and the above settings apply to the whole keyboard, but I though it was still worth a try.

I hope this helps.

Sounds to me like your keyboard might be going bad or perhaps it's very dirty/dusty. Use a can of compressed air to blow out as much crud/dust as possible concenrating especially on the backspace key area. Have another keyboard you can try?

Good luck...

You would be surprised how much dust can accumulate in your keyboard in 6 months. But since it's still under warranty that is the best approach I think also. A friend lives in Arizona and they have a lot of dust there and they blow it out every couple of months...

Good luck...