As the provided example as nearly 1000 line of custom code, it is hard to determine which part can be causing this.
My assumption is that it is connected with the Grid width, as I noticed that where there are multiple columns the last columns are outside of the Grid. This can occur if the Grid has fixed width and the scrolling is disabled.
If you share more details about the code and which part is responsible for that I will be happy to inspect it further.
Regards,
Stefan
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