Hello,
thank you for patience.
This bug should be fixed in new release(hotfix) 1.5.4.


You can also fix it by Yourself. Use %V instead of %W in date functions.

administrator/com_booking/helpers/booking.php
----
replace
$current->toFormat('%W');
with
$current->toFormat('%V');

line 810 and similar at a few other lines
----

administrator/com_booking/helpers/html.php
---
replace
$week = (int) $date->toFormat('%W');
with
$week = (int) $date->toFormat('%V');
line 662
---

Hello

the problem has disappeared yet. I appreciate the quick response.

Thanks :)