These days most smartphones come with on-screen navigation buttons, but some still come with capacitive buttons on the bezels. The quality of these buttons is not the same on every model. Most models have a good set of buttons installed, but on some models they are less sensitive and on some they are hyper sensitive. But this is not as big an issue. Since these phones are low-end budget smartphones, small inconvenience like this can be ignored and can be lived with.
But these inferior capacitive buttons sure become a reason for headache when coupled with some faulty tempered glass. A lot of people use tempered glasses to protect the screens of their smartphones. The quality of these glasses vary, and with it, their impact on the screens and the capacitive buttons vary.
When neither the glass nor the buttons are of good quality, they give rise to issues, especially when the smartphone is used for a long period and/or its temperature rises. Sometimes the response is simply delayed, but sometimes the buttons become so unresponsive that you have to try various ways of touching, sliding, taping or even hitting to register an input and sometimes multiple inputs are registered for a single touch. Moreover, there is no pattern to get used to, it is random and can cause problems.
So next time you choose a smartphone with capacitive buttons and/or buy a tempered glass, make sure to check their qualities.