This applies to weekend days. Weekdays are always shown in the weekly calendar, even when there is no working time on them. A weekend day, such as a Saturday, only appears when it has a working time, so a Saturday with a block but no working time will not show, even though the block is still saved. Nothing has been deleted.
The weekly calendar only displays the hours covered by a working time. On a weekend day that has a block but no working time, there are no hours to display, so the day collapses and the block is not visible. Adding a working time on that day gives it a time window to show, which makes the block appear again.
1. Add a working time on that day (recommended)
Give the day a visible window by adding a working time for the practitioner that covers the relevant hours.
Open Planning.
Click the green + Add button.
On the Work tab, set the date, the from and to times, and select the practitioner and location.
Click Add to save.
The day will now appear in the weekly view. If you want the time to stay reserved, keep your block within these working hours, or use the "Only allow specific appointments" toggle on the working time to limit what can be booked.
2. For recurring days, use a repeating working time
If the practitioner works the same hours on that day every week (for example every Saturday), set up a repeating working time so you do not have to recreate it each week. You can manage the repetition from the working time itself in the staff planner.
3. View the block in the planner
Even when a weekend day is collapsed in the weekly calendar, the block is still visible in the planner. You can open the planner directly from the calendar by clicking the date in the day header.
Quick diagnosis
A weekend day (such as a Saturday) is missing, and it only has a block? The day has no working time. Add one (step 1).
It happens every week on the same day? Set up a repeating working time (step 2).
Just need to see or check the block? Open the planner from the date header (step 3).