I avoided trying early kernel-4.17.x versions, but yesterday I updated from kernel-4.16.x to kernel 4.17.17-1, but frankly that change has not helped this lockup problem at all. For example, after trying direct use (with a KDE desktop if that makes any difference) for the first time with that kernel, the kernel only lasted a half an hour before I got a lockup which could only be solved by hitting the reset button! And roughly 8 hours later after that reset I got another lockup which also required a reset to regain control.
So it appears the substantial number of AMD graphics fixes in kernel-4.17.x are not sufficient to stabilize use of this AMD RX 550 graphics card that should no longer be considered cutting-edge hardware (i.e. it was first offered for sale at least 16 months ago). Because of these on-going issues with direct use of this card, I am going back to using the X-terminal method with this kernel which experience with kernel-4.16.x shows is much more stable since it avoids using this graphics card completely (except for the direct display of the Linux console login prompt). I will try again to use this card directly when kernel-4.18.x is promoted to Buster. Alan __________________________ Alan W. Irwin Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); the Time Ephemerides project (timeephem.sf.net); PLplot scientific plotting software package (plplot.sf.net); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________