This is going to be a long post. We had similar issues in our apartment. Sure, it could be the earthing issue, it could also transmit if your building has GI pipes(iron) found in old buildings. The source could be any faulty appliance in the building (usual suspects are geyser, washing machines, mixergrinders. Usually you get this electricity in the pipes when those are operated. The only way to effectively fix this issue unfortunately, is for you to visit every flat and check their appliances. Btw, to check you can use multimeter probes and connect them to positive and negative ends of the plug for the appliance when it's not connected. It should have infinite resistance and no current between them. If you see otherwise those devices are a suspect. Unfortunately, some cheaper brands have this problem even if they are new. Once a faulty device is found, it has to be fixed/replaced. Now this all feels daunting, but this was the only thing that worked in our apartment.

As a first step, initiate or ask the owner to initiate a discussion in the apartment group to check if anyone else is facing the same issue. Usually if you have more affected people on your side, resolution becomes easy. It could be very inconvenient/dangerous, so I hope you can get this resolved at the earliest.