"Delayed" Raidboss catch

Hi, got the following situation:

Raidboss 1 T5 45min left
Raidboss 2 T4 10min left

Because of lobbys we decided to do Raidboss 1 first. After defeating I ran out of the catch screen to join the lobby at Raidboss 2 in the last minute. No balls thrown.

We defeated Raidboss 2, I catch this one immediately and go back to Raidboss 1 to return to the catch screen.

Fail.

I was not able to get the catch screen again. Game created a new lobby (only me) and after 120sec "you already defeated the Raidboss" message appears.

Time between leaving and returning to Raidboss 1: 10min

What goes wrong? I can remember to read a article about "delayed" Raidboss catches and that this is possible.

Cheers

*edit
minor text fixes