Thanks for your reply. Yes, you're correct about the tool names. The solution provided via the Windows forum worked - when using the tif version, things worked as usual. As I wrote on the other forum, I usually work with tifs, but this time I was "lazy" and started in on the afphoto version. I use an ancient WACOM graphics tablet. I've been doing this a long time, but when Adobe went to their greed-based subscription mode, I found Affinity Photo and have been using it for about 2 years. BTW, when I noted this problem, I tried it with my mouse instead of the tablet, and the result was the same - an annoying lag in response. I am not tracing any drawing, I scan my rough inked drawings and then clean them up with the program. I'm using a 27" iMac with 16 GB RAM, running OS 10.13.6 (I'll move up to Mojave one of these days ...), graphics with AMD Radeon R9 M390 2048 MB.
So why does it not work correctly as an afphoto file?