FadeInSecs inconsistent with URL randomplay://tracks?

Hi there.
I need to setup a cron task that starts a player on random tracks, with fade-in (yes, I know alarm does that.)
I'm using squeezy or the telnet CLI
I generate the random playlist with "<player> playlist add randomplay://tracks",
then I expected the player would start smoothly with something like "<player> playlist index 0 100".

However this is rarely the case. Many times the player will start at normal volume without fade-in. Squeezy seems to report a timeout in the JSON client.

I examined track duration, file format and system load, however I don't see why fadeInSecs is sometimes taken into account, and often not.
The server is a Pi with an USB HDD, it isn't fast and one core is loaded at 100% for a little while when the URL is converted into a list of tracks.
I didn't find a way to generate the actual playlist without starting to play it right away (ie without using "index 0").

I would rather not step player volume over a period of time in the script, but now I am tempted to try that...

Thanks in advance for any advice.