Wierd. I’ve been using NFC Tools Pro to write to multiple tags - 2 xNTs, 2 xM1+s, and various random NTAG21x and Mifare Classic tags, and haven’t run into any trouble. Single records, multiple records. I’ve never run into any trouble.
On the iPhone side, I’m using NFC TagInfo and NFC Tools to read; both are reading everything I’ve tested without any trouble. Hardware is an iPhone 8 Plus. IIRC to use the NFC reader you have to be using at least an iPhone 7 or up… it wouldn’t work on a 6 even tho the 6 has NFC hardware in it.
What sorts of tags have you been trying with?