Cryptocurrency miners saw a modest decline in the number of bitcoins (BTC-USD) mined in September vs. August, as an increase in the network hashrate and difficulty screamed trouble for profit margins.The so-called difficulty of mining is a closely watched metric in the crypto ecosystem. It measures how hard it is to mine a bitcoin (BTC-USD) block based on the amount of participants and computing power (hashing power) used to mine and secure the blockchain. A high difficulty (as a result of high hashing power), as is the case now, tends to lower miners' profitability. Difficulty is currenting sitting around record highs at 31.36 trillion vs. 30.97 trillion a month ago, according to data from blockchain.com.The bitcoin (BTC-USD) network's hashrate, which measures how much computing power is being used to process transactions on the blockchain, is standing at an all-time high of nearly 255 exahash per second, in a move that underscores margin compression in the mining industry, according to blockchain.com data. That's up from 225 EH/s a month before. Despite a backdrop of a higher network hashrate and difficulty along with suppressed bitcoin (BTC-USD) prices, miners' revenue has edged up in September, rising to $22.4M at the end of the month from $16.6M at the beginning of the month, as per blockchain.com data. Still, that's down from $40.9M in the year-ago period. Overall, crypto miners' bitcoin (BTC-USD) production ticked down ...