Visual glitches on Chrome - but only in some places. What could be the problem?

The computer in question is one that I've set up for my mother-in-law, but I can remotely access it anytime via TeamViewer. She is only using it for browsing web via Chrome, and so far it's worked great, but lately she's complained that some websites are displaying visual artifacts. More details: * It runs Linux Mint, latest version with automatic updates. * It's an older machine - Phenom II X2 550 CPU, 6GB of RAM, Radeon 6450 GPU (passively cooled), Samsung 860 Evo SSD. Still powerful enough for web browsing. * The glitches usually are either black blocks or gray/blank areas. Kind of reminds me of GPU memory corruption, however the symptoms don't quite match. * They are reliably reproducible in the same webpages in the same places. Other webpages don't have them. * It's not a monitor glitch - I can see them over through TeamViewer. * Rebooting does not help. * Enabling experimental Vulcan support in Chrome has helped a lot, but some places still have them. * Running a few online 3D WebGL benchmarks don't exhibit any corruption * Firefox seems to run fine, but she's used to Chrome, so I'd rather not change that. * The glitches don't seem to line up with any HTML elements * The glitches scroll with the webpage * The desktop environment itself as well as other apps (that I tried at least) don't exhibit any corruption, HOWEVER: * When I tried viewing her computer over TeamViewer today, I noticed that my connection seems to freeze at times. At one point I even had to reconnect. I wanted to chalk that down to flaky internet (although we both have broadband cable), but then she told me that the freezes were happening on her side as well - so it wasn't the internet that was freezing, but rather her whole PC. I tried looking for evidence in logfiles, but all I could find was a hang and a core dump of systemd-udevd which might have lined up with the biggest freeze. Not much else to go on, but I also don't know where to look. * She also complained that lately some of the little arcade games that she likes to play on the web (solitaire, mahjong, breakout-clones, etc) have become much slower - albeit no glitches. I can't make up my mind if this feels more like a software bug or a hardware bug. Hardware bugs are usually more all-encompassing than just a single app in specific places. But visually it resembles hardware bugs and systemd-udevd is related to hardware... **Any ideas what could be the problem, or where I should look for more evidence?** Unfortunately I don't have any screenshots, but here's an interesting cellphone photo she sent me. Note in particular the cloud icons that overlap the glitches. I later connected to her computer (after it had been rebooted) and reproduced this view EXACTLY (which is another strike against hardware bugs - they're usually more random). This particular glitch went away after enabling the Vulcan support, but later she discovered other webpages that still have these glitches.