1.you might want to check your developer temperature at the end of processing. Hands can warm a solution, and ambient temp can lower or raise it. Many use a larger tray with a water bath to moderate the temp. This variable can really make your development times unreliable I learned after years of ignoring it.
2.Secondly, scratching is a big problem with wet negatives as the film corners are sharp and the emulsion is soft. I ended up using flat bottom trays with the emulsion down, others have different methods. The emulsion down or up choice is something you hear different opinions on.
3.One thing to remember is that developer sloshes over the sides of film when you put a sheet down face up in the tray, and this can give you stronger development on the edges as versus the interior portion of the neg. I found that placing the film in the developer face down gave a complete exposure to the developer all at once. The trays can scratch with emulsion down, so I got some flat bottom trays for this process.