Nextion SD Card upload problem

I have a 2,8" enhanced version which I bought about a year ago. I uploaded programs and everything worked fine. I recently tried uploading a new program via SD Card and when I switch on the power to start upload cycle it flashes a white screen 3 times then go blank. I have tried with blank project, different cards no difference.
The previous program I loaded onto screen is still there and works fine, but I cannot upload new program.
My other screens upload program no problem. This is genuine Nextion screen bought from my usual supplier.
Any ideas?
I have ordered a converter to upload directly from pc maybe that helps.
Never had any problems before, and found them to be very reliable.

Might be a power supply issue. The SD card and slot use power in addition to the usual inrush current peak. Check the power supply and cables to make sure that the 5V remain rock stable during start-up and flashing.

Thanks for the reply.
Have tested with various Power Supply’s, that’s not the problem.
My FTDI converter were delivered and I have tested it, am able to upload directly from pc without
any problems. But still same problem with SD Card. Very weird!
Thanks again for the assistance, appreciate it.
Just had a thought, I am testing solely with power connected to Display, no comm’s connected to
MCU, maybe that has something to do with it. All the ones connected to MCU’s work fine.
Probably not the issue but will test in any case.