This was a bug related to negative neighbour counts for Weighted neighborhoods. I've committed a fix to the repo. Thanks for reporting!
The main change that might be relevant in 2.8 was a switch to OpenGL for rendering.
overlay-demo - pixels demo minor change
overlay-demo - pixels demo is prettier and faster
overlay replace return changed pixel count from...
10x speed improvement for 5 overlay replace use...
Merge branch 'master' of ssh://git.code.sf.net/...
overlay replace command and demo, breakout.lua ...
overlay-demo.lua - new points demo and animatio...
overlay-demo.lua - new drawing lines test
Merge branch 'master' of ssh://git.code.sf.net/...
overlay-bricks.lua - minor updates
overlay-bricks.lua - speed increase each level ...
overlay-bricks.lua - minor updates
overlay-bricks.lua - pause if mouse leaves over...
overlay-bricks.lua - high score saving, levels,...
overlay-brick.lua - added keyboard controls and...
overlay-bricks.lua - bricks for golly
lifeviewer button images
minor updates to overlay-demo and lifeviewer
minor fix to overlay-demo
lifeviewer.lua 24 - improved timing display
overlay-demo animation now has minimum frame rate
unified cross-platform overlay DoText, lifeview...
fix some windows compiler warnings
added detailed timing information overlay-demo....
overlay DoText on windows is faster with iterator
minor updates to overlay-demo.lua
Merge branch 'master' of ssh://git.code.sf.net/...
performance improvements for overlay alpha past...
minor updates to overlay-demo.lua
added golly credits to the overlay-demo animation
new test animation for test-overlay.lua
performance improvements to overlay alpha blend...
performance improvements to overlay alpha paste...
updates to lifeviewer and test-overlay for text
removed overlay text multi-column and shadow ca...
extended overlay text functions (work in progress)
extended overlay text functions WIP
native multiline blank line fix v2
native multiline blank line fix
minor optimization to overlay updatecells
Merge branch 'master' of ssh://git.code.sf.net/...
oplus multiline clipname argument can not be 't...
Merge branch 'master' of ssh://git.code.sf.net/...
native overlay mutliline text and cellview perf...
Merge branch 'master' of ssh://git.code.sf.net/...
improved overlay text performance
lifeviewer.lua 20 - timing information
lifeviewer.lua 19 - timing and refactoring and ...
Merge branch 'master' of ssh://git.code.sf.net/...
minor lifeviewer help updates
lifeviewer.lua 18 - more help and historyfit
Merge branch 'master' of ssh://git.code.sf.net/...
lifeviewer.lua 17 - updated help and track scri...
drawstars needs fixed random seed
Merge branch 'master' of ssh://git.code.sf.net/...
Merge branch 'master' of ssh://git.code.sf.net/...
lifeviewer.lua 16 - help updates, more script c...
lifeviewer 15 - z alias for zoom
lifeviewer.lua 14 - grid lines and stars
template lifeviewer help file
cellview depth fix, lifeviewer external help start
added getinfo script command which returns patt...
minor documentation updates
Merge branch 'master' of ssh://git.code.sf.net/...
camera and celloption script commands
cellivew hex support
improve cellview layer rendering
lifeviewer.lua 10 - multistate patterns default...
cellview now has improved zoom < 1x
lifeview.lua build 9 - smooth zoom
lifeviewer.lua build 8 - autofit
user defined themes, mouse pan and zoom in life...
don't return old values from cam and theme over...
Merge branch 'master' of ssh://git.code.sf.net/...
more cellview documentation, lifeviewer.lua bui...
further cellview documentation
initial cellview documentation and lifeviewer.l...
refactored overlay cellview code
updated lifeviewer.lua to build 3
updates to lifeviewer script
extended overlay for LifeViewer in Golly
Merge branch 'master' of ssh://git.code.sf.net/...
now works with new hex support in Generations rule
updated Generations help and enabled non-Moore ...
Generations support for Hex, Von-Neumann and no...
updates to Linux build files
ninja build file to build Golly faster on Linux
rle reader should allow counts across line endings
changed access to number of live states
performance improvements for algorithm draw rou...
refactored rendering speed improvements
rendering speed improvements for grid lines
rendering speed improvements for zoom x8 with i...
fixed compiler warnings related to GL_Float
rendering speed improvements for zooms > 2x wit...
Merge branch 'master' of ssh://git.code.sf.net/...
Merge branch 'master' of ssh://git.code.sf.net/...
enforce maximum rule name length