Chosen Solution

I have purchased an old 13” MBP 2015. The SSD had failed once and I bring it to a local shop to change it and it works for a few months. Recently it is behaving weird … After upgrading the macOS to Mojave, the keyboard becomes weird! Some keys work and some keys don’t. The weirdest thing is that if I keep on clicking option key during boot, the keyboard just works! However if it sleeps later and turn back on, the keyboard turns to malfunctioning! Another weird thing is that other than CMD+S and Verbose boot, other boot key combinations do not work at all. Since I would like to boot into recovery and try to reinstall the OS, I tried CMD-R / OPTION-CMD-P-R / CMD-N / even bootable USB but all of them won’t work :( The latest status is … The machine just keeps on inputting “.” key randomly … I cannot determine which part is the problem causing such weird behavior. Does anyone have ideas?

Updated: Coconut Screencap

OK, the cycle count is not overly high so thats less likely the issue until you open it to inspect the battery. I’m suspecting the trackpad cable is not making good contact either because the connector is worn or the ribbon cable got damaged from a bang. In this series you have independent keyboard & Trackpad cables but the signals are shared within the same USB2 hub logic on the logic board. So a noisy line can interfere with the signals. Here is the needed part MacBook Pro 13" Retina (Early 2015) Trackpad Cable. Follow this guide MacBook Pro 13" Retina Display Early 2015 Logic Board Replacement to Step 6, then jump down to Step 16 taking the cover off, then jump to Step 29 removing the old cable. Clean the battery surface and the inside case and apply the new cable.