The reason why your TX wasn't accelerated by ViaBTC could be, that the fee used is lower than the purging level of their nodes so any TX that doesn't use the fee above won't be included in the block.
ViaBtc nodes do not have a different purging rate than the default one used by majority nodes. What I think is that they have a backlog of transactions they are confirming and they need to successfully mine several blocks to get to your transaction. If you follow the information given above you will be able to check if your transaction is still being accelerated by ViaBtc.
Every node has its own mempool and the purging rate also varies according to that, the purge value we see on explorers are for the default size but as far as I see, ViaBTC includes the TXs above 23sat/vbyte in their blocks constantly so I assume that could be their purge rate or I may be wrong but ViaBtc always includes the submitted TXs in their next blocks or atleast in the two and if it's taking more than that then the TX may not be submitted for acceleration.