I have a point of sale application developed in PHP Some clients have point that the system starts to hang and stuck

I have a point of sale application developed in PHP Some clients have point that the system starts to hang and stuck

issue:- I have a point of sale application developed in PHP Some clients have point that the system starts to hang and stuck when sleeted multiple items this issue occurring randomly in a specific time of the day, when it's used more often. And some time happens when click on save button while doing multiple transitions Now can anyone tell me how to reproduce this issue.

Question:- is that server side issue and need to test load and performance testing on system?