It's not a bug that I am aware of.
It could be an issue with running an unsupported version of PHP (which is why I asked what version you were running).
If you don't want to upgrade that's your decision. The version you are running is from 2017 and there have been a lot of Performance and Security fixes added since then. Just know that you are running and end of life product and will not be able to get support on it.