Adobe Creative Cloud does the update to v15.0. On opening the Project it updates and prompts to save as a new file as is normal for version updates. This Project includes 3 animation clips which are sequences of images playing at 50fps. They have changed to 25 fps. I check in preferences and the project "indeterminate media timebase" remains at 50 fps. My Workaround is to manually "re-interpret" these frame rates. Reproducible? 3 x different animations in this project have done this. However other 50fps animations in 2 x other projects converted after this one are OK.

On installing v15.0, CC prompted me for keeping previous settings and I responded yes to that. I suggest that there may be an underlying bug where settings persistence needs improvement.

Give us all the details of the system where the problems occurred: hardware model, OS, OS version, and so forth
Recently updated system new parts December 2020, Gigabyte B460M motherboard. Intel i7-10700 processor. 32 GB RAM. Nvidia 1650 Super graphics card. HDDs are 250 GB SSD for system and 500 GB SSD for data. It works well with Premiere until this update.