According to the note from 16 June of US embassy in Colombia on Security alert - second round of the presidential election process:
Roads may be closed in major cities, including Bogota, on June 19. Land and sea borders will be closed from 6:00 pm on Saturday, June 18 until 6:00 am on Monday, June 20. Alcohol sales are restricted from 6:00 pm on Saturday, June 18 until noon on Monday, June 20.
It also happened in 2018:
Colombia’s land and maritime borders will be closed ahead of the election, as is customary. Borders with Ecuador, Peru, and Brazil will be closed from 00:01 (local time) on May 26 until 16:00 on May 27, coinciding with the scheduled closure of polling stations. Border crossings with Venezuela will be closed for a longer period, from 00:01 on May 24 until 06:00 on May 28.
I also recall having read about the alcohol prohibition in other elections, not only the presidential.
Why is this? Why is Colombia closing its borders the day an election is being held?