I've found a hint to the reason. Today the epg.data file has grown to 192 MB, no wonder VDR gets OOM when it tries to read that thing. The cause seems to be duplicated X lines like this:
E 3809 1120376700 900 50 T nah & fern S Gartenreich Wörlitz / Florenz des Nordens / Fürst-Pückler-Park / Inseln mit Ch arme / Sicheres Zelten D Gartenreich Wörlitz / Florenz des Nordens / Fürst-Pückler-Park / Inseln mit Ch arme / Sicheres Zelten X 2 01 deu Mono X 1 01 deu 4:3 X 2 01 deu Mono X 1 01 deu 4:3 X 2 01 deu Mono X 1 01 deu 4:3 X 2 01 deu Mono X 1 01 deu 4:3 (and the last two lines are repeated about 4000 times).
This entry is from ZDFinfokanal, but I have many more channels where this happens.
Olaf