Poland thinks Putin is beind this and it is almost certainly right, as he was probably at least offering assistance with the Ryanair hijacking and the brutal putting down of the protests. The two men despise each other but they have other goals that draw them together. It isn't only Poland of course which is affected but possibly Putin/Lukashenko think they can cause more grief there: possibly provoke an ovferreaction. Or it may be nothing more than simple revenge: dumping your rubbish in your neighbours' gardens as he would doubtless see it. The Polish government has a big dilemma now. At the start, most people supported the clampdown on the refugees, but as time as gone by and people see what is really happening there is a growing call for a relaxation on the closed border policy with many Poles bringing supplies to the refugees. Do they continue to keep the refugees at bay or risk, albeit unfairly, being accused of being inhumane.
These people were given visas for Belarus and allowed to fly to Minsk. This has been happening since June. They even get bussed to the border by the local authorities. It's wicked and cynical but it's not clear what can be done about it.