The rectangle drawing tool is quite buggy when you use the RHS panel to switch to a different shape.
When you first draw the rectangle, it comes out fine but the shape selector is set to ‘triangle’
When you select ‘oval’, the shape successfully changes but the selector still says ‘triangle’
When you select ‘horizontal line’ the shape disappears, and selector switches to ‘vertical line’.
When you select ‘vertical line’ shape is still missing
When you select ‘triangle’ shape is still missing
Would be great if you could take a look (@Antti_Neonto/@Adam_Wasserman) when you get some time. The current workaround is to copy and paste vector shapes from older projects made with RS when each shape could be drawn with a separate tool.