Quick research suggests this timeline to me:
Summer 2014 Apigee raises last private funding at a $600M valuation
April 2015 Apigee IPOs at a valuation of $500M
By end of 2015 Apigee closes at a valuation of ~$250M.
So the company lost almost 2/3rds of its value probably right as the lockup period was expiring for employees to sell shares.