What will happen to PLC if there is no end instruction?

For example, in Mitsubishi FX2N PLC, the result of not adding END is that after scanning once, empty instructions are always executed. The CPU must meet the END instruction before it thinks that a scanning cycle is over, so it needs to be refreshed before it can start a new scanning cycle. In Siemens S7 200, the command END is added by default. Whether it is visible or not, this command definitely exists.