Push-buttons
Current PortaPack models have five push buttons on the front (UP, DOWN, LEFT, RIGHT, and SELECT) and two on the top (DFU and RESET). In most cases, a long press of a directional button will repeat automatically after a short delay (firmware may define additional behavior for a long press of any button).
If the push buttons "stick", check to make sure that the buttons are centered in the holes in the case, and are not rubbing against the inside of the holes.
If the push-buttons are intermittently unresponsive, first make sure that the Portapack firmware is upgraded to version 1.7.1. or later, which improves handling of glitchy switch contacts. The type of push-buttons used on the Portapack is SMD tactile switches of 6 mm per side and 7 mm of height. You can buy replacements here: https://a.aliexpress.com/_dZqx4vv
The easiest way to remove them is to clip the legs off, clean the pads carefully with solder wick and solder the new buttons.
You can also find replacement caps for the tactile switches: https://www.aliexpress.com/item/1005001700437278.html
Alternative caps for the switches: https://www.ebay.com/itm/284831256446