Hi @luisv,
Do you mean that all the tab index crashed when you replace all the dropdowns with radio buttons?
Could you please try to tab one time in a published version?
I have a test and the situation is confirmed on my side. If you tab within your form in a Google browser, the tab index will be in mess.
The Tab Index does not work in that way.
PowerApps really only recommends one of two values for TabIndex - either 0 or -1.
0 means it will participate as a tab stop control. -1 means it will not stop via tab.
PowerApps tabs from top to bottom, left to right in a Z pattern. The X and Y properties of the controls will determine when they are selected by tab.
If you have a control in the top left with a Y property of 2 and a control to the left of it with a Y property of 1, then PowerApps will tab from the second control to the first because it is going from top down and the second control is more "top" then the first.
You can read more about this and other options for grouping controls with the Experimental Enhanced Group Control.
As an alternative solution, I think you could set all the tab index of the Radio buttons as 0 so that each radio button will be tabbed in order if you don't have a custom tab order.