In my gear I use a ZWO filter set (7nm) bought as part of an EFW set. I regularly observe that the autofocus of the red and green filters exhibit an HFR in the range of 0.65 to 0.72, while the blue filter rarely falls below 0.88. Also, the stars in the blue-filtered images are bloated.
In a cloudynights post I found a hint that this is a "feature" of the (blue) filter. Are there similar experiences from other people in this forum? Should I replace the LRGB filters? Are there any recommendations for my ASI1600MM?

Thanks for hints.

I have the same filters and Blue usually has the most bloat. In narrowband Oiii (nearest blue) is usually worst. I don't know if its a filter thing or a refractor thing, or a combination.

Thanks John for comment. I cannot confirm that my OIII filter shows same behavior since I haven't used both OIII and SII filters for about 3 months. I want to check tonight with some test focuses of all my filters.

Does anyone in this forum have experience with Baader's Semi Apo or Fringe Killer filter against chromatic aberration from refractors in the optical train?

You are going to get some bloat... I have it also on my ZWO's.... and it's why I'm currently saving the pennies up for Chroma or Astrodon filters... but because of the cost, I simply deal with the cheaper ZWO filters. Yes, I could get some Antlia's... but honestly, I'd rather take that money and keep it aside to get some really good filters.

In the meantime I have spoken to Teleskop Service, where I bought my telescope. They admit that the telescope is probably not optimally corrected in the blue. I have now decided not to use a filter and to invest the money in a reflecting telescope that, in principle, does not exhibit this issue (if correctly collimated).

If you are using a flattener/reducer, it could also be the issue.. I have observed that some images (with an Apertura refractor) that the flattener presented issues with imaging. Getting a new flattener resolved the issue.
Investing in a "reflecting" telescope won't guarantee to resolve the issue.... what usually does is getting better quality filters. The ZWO are at best an intro level set of filters. The Antlia will do better, and then if you want to move up (which is what I'm saving for) the Astrodon/Chroma filters will be even better.
I get bloated stars on a "not so cheap" William Optics 103mm ZenithStar using an ASI533MM Pro and ZWO filters. I realize it is simply a matter of the cheaper filters and wait to build up the "kitty" to be able to afford good filters.
Bloated stars can happen even with NO filters present... as shown by this image . It was captured with an Apertura 72mm APO refractor and ASI533MC Pro with no filters present, but an Apertura flattener which I'm pretty sure is introducing some of the issue... but try to convince High Point Scientific of that. I simply am going to have to investigate a better flattener/reducer specific to that telescope and then pay for it. HighPoint doesn't offer an actual flattener/reducer for it that they admitted to... but this scope is a fairly generic one and I'm sure that I can find something that works.