That electrical tape insulator may have a short life span. Maybe change out that piece of track.
To locate the source of a short, one way is to isolate the layout with electrical blocks. Turn all toggles off then bring them back on line one at a time until the short reappears.
On small or temporary layouts pull apart collective segments of track starting furthest from power feeds.
Look for shifted middle rail insulators, pieces of train equipment touching middle rail & metal tie, nicked or broken wire, excessive insulation removed from a wire permitting + & - contact.
Remove roller equipped engines/cars one at a time while checking for short.