Cannot tq_mutate with TTR function for cryptocurrency but can with stocks

[noahmthomas-nmt]

I get an error when running:

rbind(tq_get("BTC-USD"),
tq_get("ETH-USD")) %>%
group_by(symbol) %>%
tq_mutate(select = close, mutate_fun = RSI)

Error: Problem with mutate() input nested.col.
x Series contains non-leading NAs
i Input nested.col is purrr::map(...).
i The error occurred in group 1: symbol = "BTC-USD".
Run rlang::last_error() to see where the error occurred.

But not when running identical code with stock tickers instead:

rbind(tq_get("MSFT"),
tq_get("AAPL")) %>%
group_by(symbol) %>%
tq_mutate(select = close, mutate_fun = RSI)

Very confused by this.