Some Russian puzzles are unsolvable in the app.
Both puzzles are solvable in the browser, but 'hang' on the ambiguous King jump near the end.
The main variant contains a King Jump that can be executed in two ways from the same source square to the same target square but taking a different amount of pieces.
Also the wrong, not winning, capture with the less pieces 'hangs' as if in the winning continuation but offering no reply for black. The only way to continue is to forfeit the puzzle and accept the rating penalty.
@dg If you are solving Russian puzzles with specific fly-through promotion idea (like #27 and #254), you should consider enabling a mode with gradual capturing. Go to "Preferences" -> "Game behaviour" -> and at section "How do you play multi-captures on analysis boards?" check "Step by step". The idea is that you must CLEARLY indicate a jumping path if there are controversial options, and, for comparison only, in serious tournament an arbiter has rights to issue a warning to a player if he or she neglects to indicate correct capturing sequence while recording a game. Partial indication is acceptable, for example, at Russian puzzle #254 5. h4:d8:h8 is tolerated.
The multi-capture setting is indeed a bit confusing with Russian draughts and I messed up several puzzles in the beginning but I don't think changing this setting wil solve the issue in this case. I have the same setting in the browser as in the app.
The issue here is that I can execute the correct jump, but the app does not present a black continuation after the capture and just shows: 'find the best move.' Also in the case of the wrong jump that shows in the browser that you failed the puzzle, on the app just says 'find the best move' and offers no black move.
It is really a bug in the app.
@dg I can confirm this is a bug in the app, I have the same problem with the puzzles you link.
However it only happens when the multi-capture setting is on 'All at once', I can complete the puzzle fine when performing the capture 'Step by step'.
Will get that fixed in the next update, thanks for reporting
Ah interesting, user kalnap suggested also such a thing, but I could not test it yesterday.
I will keep it in mind to change the setting as soon I get a puzzle like that.
Thanks for the great work.