I have same error in 15i, but I repair by setting "act_second_tab3_x=205" in coordinates.ini
I think that parameters name should be more smart because act_second_tab3_x doesnt tell for what tab it used.
I propose follow format:
difficulty_%DIFFICUTY%_opened_%OPENED_COUNT_ON_tHIS_DIFFICULTY%_act_%ACT_NUMBER%_x
eg:
dufficulty_normal_opened_3_act_2_x
or
dufficulty_normal_opened_3_act_2_tab_x
And parameter of difficulty tab will be as:
difficulties_1_difficulty_normal_tab_x