There is a big increase for Belarus between 4/1/20 and 4/14/20. According to https://en.wikipedia.org/wiki/COVID-19_pandemic_in_Belarus the first reported case was Feb 28, the first death was Mar 31st. On Apr 4 the spring vacation for schools was extended for a week (it was later extended on Apr 10 for another week). Maybe the school spring vacation corresponds to the increase in IPDV between 4/1/20 and 4/16/20. Following 4/1`616/20 it appears the IPDV drops below previous levels going back to 1/20/20.
For Poland there appears to be an increase in IPDV between 3/6/20 and 3/16/20. The 1st case was reported Mar 4t, the first death Mar 12. Between 10-12 Mar lockdown measures were announced that closed schools, universities and mass events.
The increased IPDV between 3/6/20 and 3/16/20 is seen more clearly in the alldays days data if we highlight the Poland line and change the y-scale for IPDV: