Can filing a section 217 election ever increase the tax I owe instead of reducing it?

Yes, it can. A section 217 election isn't automatically a tax break, it changes how your Canadian pension-type income is taxed, from a flat withholding rate to graduated Canadian rates applied with reference to your worldwide income, and that combination can work out worse than the flat withholding if your total income, from all sources and countries, is high. The election was designed to help people whose Canadian income makes up most of their livelihood, not necessarily to benefit every non-resident who receives some Canadian pension income.

Because the calculation requires disclosing your worldwide income to CRA to work out the applicable rate and credits, someone with substantial income earned elsewhere may find that electing pushes their effective tax on the Canadian income higher than simply accepting the flat withholding that would otherwise apply.

This is exactly why the election is optional rather than automatic: nothing forces you to make it, and if a proper comparison shows it would leave you worse off, the sensible choice is simply not to elect and let the standard withholding stand as your final tax on that income. Running the numbers before deciding, rather than assuming the election is always favourable, is the important step here.