Sitemap not visible when using specific item?!


I´m running openhab on raspberry PI 4 version 3.2 and since one of the last updates I am having a problem with my sitemap on iOS (browser on PC/MAC as well).

Here´s the code of my sitemap:

Group item=gWetterdaten label="Komfort & Wetterdaten" icon="sun_clouds"{

Frame label="KWL" {
Switch item=Wohnraumlueftung label="Wohnraumlüftung" icon="kwl"
Text item=Taupunkt_Keller label="Taupunkt Keller [%.2f°C]" icon="dewpoint_inside"
Text item=Taupunkt_Aussen label="Taupunkt Außen [%.2f°C]" icon="dewpoint_outside"
Text item=Taupunkt_EG label="Taupunkt Erdgeschoss [%.2f°C]" icon="dewpoint_inside"
Text item=Taupunkt_OG label="Taupunkt Obergeschoss [%.2f°C]" icon="dewpoint_inside"
Text item=Taupunkt_Differenz label="Taupunkt Differenz KG [%.2f°C]" icon="dewpoint_difference"
Text item=Taupunkt_Differenz_EG label="Taupunkt Differenz EG [%.2f°C]" icon="dewpoint_difference"
Text item=Taupunkt_Differenz_OG label="Taupunkt Differenz OG [%.2f°C]" icon="dewpoint_difference"
Text item=Wohnraumlueftung_Start_Time label="Letzte Startzeit KWL [%s]"
Text item=Wohnraumlueftung_Stop_Time label="Letzte Stoppzeit KWL [%s]"

When the first Item “Switch Wohnraumlueftung” is active the hole Group item is blank. Not a single item.
As soon as I´m deleting (or disable with “//”) the Group item is displayed correctly.
I am using this switch in several locations on my sitemap and the problem is in all places.

Any idea how to fix this? The log viewer doesn´t show any error or additional informations.

Thank you!

Edit: Here´s the item definition:

Switch                Wohnraumlueftung                         "Wohnraumlüftung"                                                     {alexa="Lighting"}

Does the kwl icon exist? What happens if you remove this part from your Switch definition in the sitemap?