Hi @Randy,
Samsung stock firmware is available on various channels. Two reputable ones are sammobil and samfrew. Samfrew has the slightly faster free download, but it still takes hours to download the zipped 4.6 GB ROM.
Right now I can’t tell you why you might be having such “big problems” because your details are too skimpy and not specific enough for me. The number of possible firmware versions is too large, so first tell me which bootloader version is installed on your Galaxy S9+. It can be found under > About > Software Info > Buildnumber QP1A …G965F… The baseband version can also help: G965F…