I had trouble applying the 0.35.0 BMC firmware update to a C2750D4I with Chrome. No File browser appeared. Was only able to recover by unplugging the machine, so not something to try remotely.
Worked fine with Edge.
Here is BMC v18.00 for the affected ASRock board E3C224D4I-14S. I received this from William at ASRock and it fixed this issue for me. The hardest part was finding a damn browser that would actually flash it. After trying Chrome, Chromium, Edge, Firefox, Safari & IE, Internet Explorer 11 finally was able to upload the image and flash it. Good luck!
I got an BMC Update for the ASRock Rack E3C232D2I from the Asrock Support some time after this problem occured. It is still not on their website, but worked for me without any problems for months now. I hope this will help someone.
On the website is 07.07.00, in the download is 7.11.00