Welcome in the forum, Jan!
There is no (!!) HFCLK in deep sleep phase, so no component using it will need to set to _Sleep() and _Wakeup().
Can you show exactly where you found that wrong documentation, I would like to have Cypress cleaning that up.
I'm aware of the fact that there is no HFCLK in deep sleep. I learned that from the documentation (e.g.: AN86233, Ch2/Table2, sect 3.2.2). From section 17.2.5 of the psoc4ble trm I learned that the power is still on so the configuration of the TCPWM is kept. So, the documentation is in line with your reaction.
Why then can't I resume usage of the TCPWM after wake-up from deep sleep without doing anything? I need to use the _Sleep() and _Wakeup() for proper operation.
I would suggest you to get in contact with Cypress directly: At top of this page select "Design support -> Create a Support Case" and ask your question. You will be helped by a Cypress engineer.