Thanks, Simon, for the quick fix. It seems to work.

This actually already applied to the 0.9.7 but I've never realized it:
If you put level files in the replay folder and select them from the replay browser the game crashes with Access Violation. In earlier versions there was no problem and it's a bit nasty to have a plain crash just upon selection there.
(This crash happens in the provided binaries as well.)

Full error message (debug build, Win 7):

Lix version:  0.9.8
Session date: 2018-01-15 20:06:35
    30.37 :0:
    30.37 Access Violation
    30.37 0x005105F9 in void menu.browser.replay.BrowserReplay.onFileHighlight(immutable(file.filename.base.IFilename)) at C:\...\LixD-master0_9_8\src\menu\browser\replay.d(82)
0x005112FD in void menu.browser.select.BrowserHighlightSelect.highlight(immutable(file.filename.base.IFilename)) at C:\...\LixD-master0_9_8\src\menu\browser\select.d(58)
0x00511418 in void menu.browser.select.BrowserHighlightSelect.onPickerExecuteFile(immutable(file.filename.base.IFilename)) at C:\...\LixD-master0_9_8\src\menu\browser\select.d(84)
0x0050F32B in D4menu7browser6highli16BrowserHighlight__T6__ctorTC3gui6picker8tilerlev11ReplayTilerZQBrMFxAyay9685BBFB3F63E9BE4E3A4927E21906FF at C:\...\LixD-master0_9_8\src\menu\browser\highli.d(41)
0x004F3A72 in D3gui6pickerQh6Picker__T6__ctorTCQBgQBf8tilerlev11ReplayTilerZQBmMFSQCpQCoQCr__T12PickerConfigT84DD4EB3876DF06FF7B69392533B73CC at C:\...\LixD-master0_9_8\src\gui\picker\picker.d(72)
0x004F6B07 in void gui.picker.tiler.FileTiler.calcSelf() at C:\...\LixD-master0_9_8\src\gui\picker\tiler.d(133)
0x004EB0BC in void gui.element.Element.calc() at C:\...\LixD-master0_9_8\src\gui\element.d(124)
0x004EB407 in void gui.element.Element.calc().__lambda1!(gui.element.Element).__lambda1(gui.element.Element)
0x004EB448 in void std.algorithm.iteration.each!(gui.element.Element.calc().__lambda1).each!(gui.element.Element[]).each(ref gui.element.Element[]) at C:\D\dmd2\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(944)
0x004EB0B4 in void gui.element.Element.calc() at C:\...\LixD-master0_9_8\src\gui\element.d(123)
0x004EB407 in void gui.element.Element.calc().__lambda1!(gui.element.Element).__lambda1(gui.element.Element)
0x004EB448 in void std.algorithm.iteration.each!(gui.element.Element.calc().__lambda1).each!(gui.element.Element[]).each(ref gui.element.Element[]) at C:\D\dmd2\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(944)
0x004EB0B4 in void gui.element.Element.calc() at C:\...\LixD-master0_9_8\src\gui\element.d(123)
0x004EB407 in void gui.element.Element.calc().__lambda1!(gui.element.Element).__lambda1(gui.element.Element)
0x004EB448 in void std.algorithm.iteration.each!(gui.element.Element.calc().__lambda1).each!(gui.element.Element[]).each(ref gui.element.Element[]) at C:\D\dmd2\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(944)
0x004EB0B4 in void gui.element.Element.calc() at C:\...\LixD-master0_9_8\src\gui\element.d(123)
0x004F96E6 in void gui.root.calc() at C:\...\LixD-master0_9_8\src\gui\root.d(96)
0x00428C2F in void basics.mainloop.MainLoop.calc() at C:\...\LixD-master0_9_8\src\basics\mainloop.d(159)
0x0042898B in void basics.mainloop.MainLoop.mainLoop() at C:\...\LixD-master0_9_8\src\basics\mainloop.d(82)
0x0050E540 in int main.main(immutable(char)[][]).__lambda2() at C:\...\LixD-master0_9_8\src\main.d(39)
0x00530453 in extern (C) int allegro5.system.al_run_allegro(scope int delegate()).main_runner(int, char**) at C:\Users\...\AppData\Roaming\dub\packages\allegro-4.0.1_5.2.0\allegro\allegro5\system.d(45)
0x00530437 in int allegro5.system.al_run_allegro(scope int delegate()) at C:\Users\...\AppData\Roaming\dub\packages\allegro-4.0.1_5.2.0\allegro\allegro5\system.d(62)
0x0050E4F3 in _Dmain at C:\...\LixD-master0_9_8\src\main.d(35)
0x0053D933 in void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll().__lambda1()
0x0053D8F7 in void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll()
0x0053D7F8 in _d_run_main
0x0050E56C in main at C:\...\LixD-master0_9_8\src\verify\counter.d(7)
0x0057C119 in mainCRTStartup
0x7660337A in BaseThreadInitThunk
0x77C19882 in RtlInitializeExceptionChain
0x77C19855 in RtlInitializeExceptionChain

Just for documentation:
"Flower Towers" is mainly a jumping level and one where I fiddled around until it worked in tumbler-rewrite and the stable branch. I've made a comparision picture from a certain (late) point in the level to give an impression of the differences between the two branches. Most of the level is done by this point and it's after having done 13 jumps.
Left is the stable 0.9.7 and right the tumbler-rewrite branch. I've put the picture in a zipfile to avoid spoilers but I don't think it is spoilery.

After reading mobius' problems with copying the output from the cmd prompt:
That's one of the reasons why I want to use logfiles for building because I can copy the output (esp. error messages) conveniently from the text files.
Copying from cmd prompt seems convoluted and unintuitive for a Win user. (I know one method is: right click -> choose mark -> mark with mouse movement+ hold left click or with arrow keys+ hold Shift -> press Enter => now the marked text should be in copy buffer and can be pasted.)

Since I probably can't really care for ClamLix from February on:
If there are any physics changes that break replays, please don't only look if there is a solving replay at all but also that Clam's intended route (Clam's replays) gets a replay as well.
The levels where that is relevant are:

Arcane:
- "Beaten into shape"
- "Builders Without Borders"
- "Over and Under and Out"
- "Send in the Square Squad"
- "Turning the Screws"

Insane:
- "Dig This!"
- "Lix Recycling Plant"

Flingsane:
- "Lost?"
- "Polar Pop"

Outtakes:
- "Just drop in!"
For "Just drop in!" it would be nice if in case my alternative route would get a repaired replay as well since the route is significantly different/ a completely different way to solve the level.

Flopsy has uploaded two further videos:

Cunning 1+2
Cunning 3-5

Thanks, Simon, for your answer.