In mid-January, Eventbrite co-founder and CEO Julia Hartz gathered staff at the company’s San Francisco headquarters to lay out her strategy for the year ahead. A few months removed from the excitement of going public, Ms. Hartz described ambitious plans to expand into dozens of overseas markets and grow faster in existing ones.

But these goals ignored signs that Eventbrite’s core business was slowing, insiders say, and overlooked challenges that have since forced management to scale back ambitions. Eventbrite has launched in just three new non-U.S. markets in recent months: Singapore, Mexico and Hong Kong, with plans for others pushed back indefinitely or abandoned altogether.