Not sure why this would happen after an IPL. I have had occasions where networking with Windows 98 has stopped behaving itself and I’ve had to install additional network protocols to rectify the situation. My guess would be it’s probably coincidence with the IPL.
For Windows 98 I have always had to add the local systems into the “hosts” file in C:WindowsSystem32. This acts as a local DNS file for Windows and I would suggest you check that the System name is in there correctly.
All the best
Since you don’t tell us what OS version/release you’re running nor how your interfaces are defined on your AS/400 nor what your domain configuration is on your AS/400 nor what entry you added to the DNA other than “s10a####” which is almost certainly wrong, it’s hard to guess.