Using the Default or Material Kendo Theme (v5.6.0) with the Telerik HTML5 Report Viewer, the Boolean parameter which uses a Checkbox for it's display, is not visible (this may affect other themes as well).
I confirmed an older version v4.40.0 has a height and width set for the k-checkbox CSS class as such:
https://unpkg.com/@progress/kendo-theme-material@4.40.0/dist/all.css
.k-checkbox { border-radius: 2px; margin: 0; padding: 0; width: 16px; height: 16px; line-height: initial; border-width: 2px; border-style: solid; outline: 0; box-sizing: border-box; background-position: center; background-repeat: no-repeat; background-size: contain; display: inline-block; vertical-align: middle; position: relative; cursor: pointer; -webkit-appearance: none; }
while the latest v5.6.0 does not:
https://unpkg.com/@progress/kendo-theme-material@5.6.0/dist/all.css
.k-checkbox { margin: 0; padding: 0; line-height: initial; border-width: 2px; border-style: solid; outline: 0; background-position: center; background-repeat: no-repeat; background-size: contain; display: inline-block; flex: none; vertical-align: middle; position: relative; cursor: pointer; -webkit-appearance: none; }
The checkbox is actually on the page, but is so small it's basically invisible and completely unusable, requiring a manual CSS override to fix.