Yep. I experience this too.
I run a SQL statement to clean out my Activities Window.
Make sure to test this out in a test environment before using in Production.
Here's the SQL Statement I run (replacing <client> with my client):
delete from EJ where EJ_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900);
delete from EFC where EFC_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900);
delete from EPDC where EPDC_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EPD where EPD_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EPPF where EPPF_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from ESTP where ESTP_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EEC where EEC_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EQT where EQT_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EET where EET_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from ETI where ETI_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPOP where EJPOP_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EOI where EOI_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EEDB where EEDB_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPFV where EJPFV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPVA where EJPVA_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPPC where EJPPC_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPOV where EJPOV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPPF where EJPPF_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPPA where EJPPA_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EPUDA where EPUDA_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPCV where EJPCV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPPO where EJPPO_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPPV where EJPPV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EV where EV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from ERB where ERB_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from ECV where ECV_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EJPP where EJPP_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EPUD where EPUD_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from ERET where ERET_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EVP where EVP_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EY where EY_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );
delete from EH where EH_AH_IDNR in (select EH_AH_IDNR from EH where eh_client = <client> and EH_Status = 1900 );