Here’s what’s happening: When you press a key mapped to LSHIFT(Key_7), Kaleidoscope sends two HID Keyboard reports in rapid succession to the host. First, one with just shift, then one with both shift and 7. The RDP client will sometimes batch those HID reports together if they come in too fast relative to its update frequency for the connection to the remote host. And Windows processes the HID report in keycode order, so it notices changes in the modifiers last.
There are some things you can try, and I believe Microsoft is fixing the problem in the next version (finally). In the meantime, there are some things you can try. See the following:
Also this: Keypresses are wrong over RDP · Issue #87 · keyboardio/Model01-Firmware · GitHub