Vinegar Warning: Pay Attention to Vinegar Labels for Pickling and Preserving
gardening.org
If you've seen warnings about 4% vs. 5% vinegar for canning, heed them! Experts are sounding the call: Home canners MUST check vinegar labels for acidity.

TL;DR: Vinegar is being sold at concentrations unsafe for preservation without proper warnings, 4% vinegar is unsafe while 5% is safe to can and pickle with.