preciphs

In my experience, choice of development is too significant a factor to ignore. The choice of developer, time, method of agitation, temperature, etc., really impact the results obtained with any given film.

The 50/1.8 is a rather common and relatively inexpensive item. You may find it worthwhile to stick with your 1.4 or, if you wish, replace the 1.8; btw, the 1.8 was manufactured in several different styles.

The major "pro-lab" in RI is ABAR in Providence. The service is fast but the prices are steep. Before I opened my darkroom, I had ABAR develop b&w. Again, the cost is steep. Only (years later) after printing the negs myself was I satisfied. (This is not so much a reflection of the lab as the reality of dealing with B&W. DIY if possible.)

Red filters are notorious for fooling many TTL meters (usually resulting in underexposure). Underexposure can cause grain issues. As others have explained above, it is best to use the filter factor (meter without a filter, adjust the settings for the filter factor, then add the filter and make the exposure).

 

Next time, take at least one shot without the filter and compare the results with the shots with filter. From that, you should be able to figure out whether the filter or the processing alone is responsible for the grain.

 

Develop yourself if remotely possible!