Previous defaults of sizes of HTTP and DB pools were 50. That's not correct as some DB connections are used in the background (sending of email notifications, compute engine and others).
Recommended settings are: size(DB) ~= 1.2 * size(HTTP)
So default size of DB pool must be increased to 60 :
Be careful that HTTP and HTTPS are two different pools. When enabling both, then size(DB) = 1.2 * (size(HTTP) + size(HTTPS)) :