In my situation which is probably "not normal"... I have two checking accounts. While doing the tax software I checked the box that I did not receive the $1400 stimulus. It wasn't a week later after sending my taxes in that the IRS mailed me a notification statement of the $1400 stimulus payment. (the statement was notifying me that they sent me $1400 a year earlier!). Sure enough I checked my secondary bank statement from a year ago and there it was. The IRS caught my "mistake" on my taxes and sent me a correction to my 1040 and I had to basically pay it back. All of this occurred before April 15th.
I would be very worried if you receive a physical check. The way the postal system is working I could see checks being stolen out of the mail system. But, if you did receive a stimulus the IRS should have sent a statement in February of this year that they sent you one. I cannot see a thief stealing a check and the IRS notification statement that you were sent the stimulus... unless, thinking more sinister a roomie has access to your mail.
I would be very worried if you receive a physical check. The way the postal system is working I could see checks being stolen out of the mail system. This, bigtime. I NEVER rely on the Post office for checks or payment. I have the IRS direct deposit anything they owe me. Whenever I pay them, I pay them through their online portal and send in the paperwork/returns later. A digital trace of an IRS email beats a paper trace through the post office anytime.